- Cherry-picked from `mvestergaard:branch-protection-dev-merge`
- https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4220

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

Closes #17012

This is a combination of 3 commits.

- Update the bare repositories info/attributes if the default branch is updated
- Check the diff attributes of a file before showing a diff
- Update CHANGELOG

Code is based on Project Webhooks, removing deprecations and without
commits listing.

The avatar logic has been moved from Project to Repository as this makes
caching easier. The logic itself in turn has been changed so that the
logo file names are cached in Redis. This cache is flushed upon pushing
a commit but _only_ if:

1. The commit was pushed to the default branch
2. The commit actually changes any of the logo files

If no branch or commit is given the cache is flushed anyway, this
ensures that calling Repository#expire_cache without any arguments still
flushes the avatar cache (e.g. this is used when removing a project).

Fixes gitlab-org/gitlab-ce#14363

`Issues::CloseService#execute` signature has changed, because of using
keyword parameter for commmit.

Otherwise Rubocop will give a warning.

As mentioned in !3197.

This keeps all the cache expiration code in a single file/class instead
of spreading it all across the codebase.

Instead of flushing the behind/ahead counts for all branches upon every
push we now only flush the cache of branches that actually need to have
these statistics recalculated. There are now basically 2 scenarios and
their effects:

1. A user pushes a commit to the default branch, this results in the
   cache being flushed for all branches.
2. A user pushes to a non default branch, this results in _only_ the
   cache for that branch being flushed.

The existing code (Repository#expire_cache) remains backwards compatible
with the previous behaviour, the new behaviour is only applied when a
branch name is passed as an argument. This ensures that when for example
a project is deleted the cache for all branches is flushed.

This caches the output of the following methods:

* Repository#empty?
* Repository#has_visible_content?
* Repository#root_ref

The cache for Repository#has_visible_content? is flushed whenever a
commit is pushed to a new branch or an existing branch is removed.
The cache for Repository#root_ref is only flushed whenever a user
changes the default branch of a project. The cache for Repository#empty?
is never explicitly flushed as there's no need for it.

- Enable CI by default for all new projects

If a branch is deleted with an open merge request, amended offline, and then pushed again,
GitLab doesn't bother to update the merge request even though the last commit ID and/or
code may have changed. This MR ensures that each push will update any relevant merge
requests and adds a system note if this happens as well.

Closes #2926

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

I also revamped the tests on "closing reference commits" (= "Fixes #xxxx" for example).
Now, there are two different contexts:
- when the commits with "closing reference" are pushed to the default branch,
- when the commits with "closing reference" are pushed to a non-default branch.

Closes gitlab-org/gitlab-ce#2190.

This reverts commit 5daf44b7, reversing
changes made to 2f706fbd.

This reverts commit 435f680b.

This reverts commit 957e849f, reversing
changes made to 6b9dbe9f.
Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>