Memoize CI config node validator to prevent leaks

## What does this MR do?

This MR memoizes CI configuration node validator, to prevent possible memory leak described in #20698.

## Why was this MR needed?

See #20698

## What are the relevant issue numbers?

Closes #20698

## Does this MR meet the acceptance criteria?

- [ ] ~~[CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added~~
- [ ] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [ ] ~~API support added~~
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5733

Active tense test coverage

Fixes all tests to use active tense and follow [Four Phase Test]( https://robots.thoughtbot.com/four-phase-test#all-together)

See merge request !5233

Remove offending empty line to make rubocop happy

see https://gitlab.com/gitlab-org/gitlab-ce/builds/2931496

See merge request !5732

See merge request !5712.

Remove legacy Ci::StaticModel we do not use anymore

## What does this MR do?

This removes class that according to our code coverage report and
`grep` is a legacy and unused class.

See merge request !5710

Enable some Rubocop cops related to new lines

## What does this MR do?

This MR enabled two additional Rubocop cops:

Keeps track of empty lines around block bodies.  
`Style/EmptyLinesAroundBlockBody`

Keeps track of empty lines around method bodies.  
` Style/EmptyLinesAroundMethodBody`

See merge request !5637

Add newlines styleguide for Ruby code 

See merge request !5636

Update version_sorter and use new interface for faster tag sorting

See merge request !5723

Enable/Disable Deploy keys for a project

Closes #20123 

## Does this MR meet the acceptance criteria?

- [X] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [X] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [X] API support added
- Tests
  - [X] Added for this feature/bug
  - [X] All builds are passing

See merge request !5647

Stop 'git push' over HTTP early

Before this change we always let users push Git data over HTTP before
deciding whether to accept to push. This was different from pushing
over SSH where we terminate a 'git push' early if we already know the
user is not allowed to push.

This change let Git over HTTP follow the same behavior as Git over
SSH. We also distinguish between HTTP 404 and 403 responses when
denying Git requests, depending on whether the user is allowed to know
the project exists.


See merge request !5639

"This file is managed by gitlab-ctl. Manual changes will be erased!"

## What does this MR do?

This merge request replaces the word "gitlab.yml" with the word "gitlab.rb" in one section of the admin area.

## Are there points in the code the reviewer needs to double check?

No.

## Why was this MR needed?

Configuration is no longer done in gitlab.yml, which is overwritten by gitlab-ctl.

## What are the relevant issue numbers?

None.

## Screenshots (if relevant)



## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [x] All builds are passing
- [X] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [X] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [X] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5600

Enable Style/EmptyLinesAround Module/Class Body cop

## What does this MR do?
Enable a new rubocop cops as discussed here: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/1877/diffs#note_13021078

## Are there points in the code the reviewer needs to double check?
May be a good idea to send a message to people to prevent `master` red because of the new cop.

## Why was this MR needed?
We want to improve code style and not waste endbosses time checking style manually

## What are the relevant issue numbers?

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5692

Revert "Defend against 'Host' header injection"

We reverted this in omnibus but forgot to do it in the source NGINX template.

See merge request !5706

Enable Style/SpaceAroundEqualsInParameterDefault cop

## What does this MR do?
Enable a new rubocop cops as discussed here: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/1877#note_13529646

## Are there points in the code the reviewer needs to double check?
May be a good idea to send a message to people to prevent master red because of the new cop.

## Why was this MR needed?
We want to improve code style and not waste endbosses time checking style manually

## What are the relevant issue numbers?

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5693

Log base64-decoded PostReceive arguments

The change to base64-encoding the third argument to PostReceive in
gitlab-shell made our Sidekiq ArgumentsLogger a little less useful.
This change adds decoded data to the log statement.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/20381


See merge request !5547

Support pending invitation project members importing projects

Adds support for pending invitation project members on Import/Export - previously the import would fail.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/19973

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5683

Optimize "cache_key" using a concern

## What does this MR do?

This MR adds a concern (used by Issue and Note) that provides an optimized version of Rails' `cache_key` method. See 77c8520e for more details.

## Are there points in the code the reviewer needs to double check?

No, though a spell check would be appreciated.

## Why was this MR needed?

When loading a lot of data from Redis (e.g. an issue with lots of notes) quite a large amount of time is spent in generating cache keys. This is due to multiple reasons such as:

* Rails trying to figure out if it should use `updated_at` or `updated_on` using somewhat inefficient code
* Rails relying on pluralization logic to figure out how to generate a cache namespace using a model name
* Rails calling a whole bunch of methods in general in the process of generating cache keys

In short, Rails is trying to cater to every possible use case, at the cost of performance.

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/13651 is not directly related but I ran into this `cache_key` problem when looking into said issue.

See merge request !5715

Update templates

There was a copy pasta in the templates, therefor another MR with updates.

See merge request !5714

This concern provides an optimized/simplified version of the "cache_key"
method. This method is about 9 times faster than the default "cache_key"
method.

The produced cache keys _are_ different from the previous ones but this
is worth the performance improvement. To showcase this I set up a
benchmark (using benchmark-ips) that compares FasterCacheKeys#cache_key
with the regular cache_key. The output of this benchmark was:

    Calculating -------------------------------------
               cache_key     4.825k i/100ms
          cache_key_fast    21.723k i/100ms
    -------------------------------------------------
               cache_key     59.422k (± 7.2%) i/s -    299.150k
          cache_key_fast    543.243k (± 9.2%) i/s -      2.694M

    Comparison:
          cache_key_fast:   543243.4 i/s
               cache_key:    59422.0 i/s - 9.14x slower

To see the impact on real code I applied these changes and benchmarked
Issue#referenced_merge_requests. For an issue referencing 10 merge
requests these changes shaved off between 40 and 60 milliseconds.

Branch permissions layout

CE part of https://gitlab.com/gitlab-org/gitlab-ee/issues/179

Related javascript code has been refactored and also layout has been updated.

![Screen_Shot_2016-08-04_at_3.23.19_PM](/uploads/a0f6165e255b3f93dcb80eaa3f3318e4/Screen_Shot_2016-08-04_at_3.23.19_PM.png)


See merge request !5652

Add migration-related tips to the "Merge Request Guidelines" doc

## Why was this MR needed?

To avoid issues like #20606 cropping up again.

See merge request !5700

This reverts commit 47b5b441.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/17877#note_13488047

Document that webhook secret token is sent in X-Gitlab-Token HTTP header

## What does this MR do?

Note that the secret token is sent in the X-Gitlab-Token header on the webhook documentation page, as well as directly below the secret token field on the webhook settings form.

## Are there points in the code the reviewer needs to double check?

No.

## Why was this MR needed?

It took me a while to figure out how to verify the token in my hook endpoint. Issue #18256 is where I found how to do it.

## What are the relevant issue numbers?

#18256 

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)
Closes #18256

See merge request !5664

fix: respect data-attribute 'skip-users' in user_selects

Backport https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/604 to CE, so that JS file is the same in both versions. Thanks @hwdegroot!

No CHANGELOG needed because this code path isn't used anywhere in CE at the moment.

See merge request !5685

Simplify feature introduction note



See merge request !5705

[ci skip]

[ci-skip]