Instead calling diff_collection.count use diff_collection.size which is cache on the diff_collection

Introducing the concept of SafeDiffs which relates 
diffs with UI highlighting.

Speedup DiffNote#active? on discussions, preloading noteables and avoid touching git repository to return diff_refs when possible

- Preloading noteable we share the same noteable instance when more than one 
discussion refers to the same noteable.
- Any other call to that object that is cached in that object will be for any 
discussion.
- In those cases where merge_request_diff has all the sha stored to build a diff_refs get that 
diff_refs using directly those sha instead accessing to the git repository to first get the 
commits and later the sha.

Now we link to the standard `IssuesController#new` action, and let it
redirect if we're using an external tracker.

Prior, in order to display the correct link to "Issues" in the project
navigation, we were performing a check against the project to see if it
used an external issue tracker, and if so, we used that URL. This was
inefficient.

Now, we simply _always_ link to `namespace_project_issues_path`, and
then in the controller we redirect to the external tracker if it's
present.

This also removes the need for the url_for_issue helper. Bonus! 🎉

Provide more sensible default sort order for issues and merge requests
based on the following table:

| type           | state  | default sort order |
|----------------|--------|--------------------|
| issues         | open   | last created       |
| issues         | closed | last updated       |
| issues         | all    | last created       |
| merge requests | open   | last created       |
| merge requests | merged | last updated       |
| merge requests | closed | last updated       |
| merge requests | all    | last created       |

This MR adds a string (thus max 255 chars) field to the enviroments
table to expose it later in other features.

1. It makes sense to reuse these constants since we had them duplicated
   in the previous enum implementation. This also simplifies our
   `check_access` implementation, because we can use
   `project.team.max_member_access` directly.

2. Use `accepts_nested_attributes_for` to create push/merge access
   levels. This was a bit fiddly to set up, but this simplifies our code
   by quite a large amount. We can even get rid of
   `ProtectedBranches::BaseService`.

3. Move API handling back into the API (previously in
   `ProtectedBranches::BaseService#translate_api_params`.

4. The protected branch services now return a `ProtectedBranch` rather
   than `true/false`.

5. Run `load_protected_branches` on-demand in the `create` action, to
   prevent it being called unneccessarily.

6. "Masters" is pre-selected as the default option for "Allowed to Push"
   and "Allowed to Merge".

7. These changes were based on a review from @rymai in !5081.

1. The model now contains this humanization data, which is the once
   source of truth.

2. Previously, this was being listed out in the dropdown component as well.

1. Move to dropdowns instead of checkboxes. One each for "Allowed to
   Push" and "Allowed to Merge"

2. Refactor the `ProtectedBranches` coffeescript class into
   `ProtectedBranchesAccessSelect`.

3. Modify the backend to accept the new parameters.

1. Improve error handling while creating protected branches.

2. Modify coffeescript code so that the "Developers can *" checkboxes
   send a '1' or '0' even when using AJAX. This lets us keep the backend
   code simpler.

3. Use services for both creating and updating protected branches.
   Destruction is taken care of with `dependent: :destroy`

Before when you choose the way of `sort` instead it display the title correctly it was just apply the humanize helper in sort value.

E.g.

When you choose `Last updated` it should display the title `Last updated` instead of `Recently updated`. This fix makes this correctly displays the title.

Change the implementation of the `link_to` `filter_branches_path`

- Change the value of the `params[:sort]` in `link_to`. E.g. instead of using `'recently_updated'` is now using `sort_value_recently_updated`.

- Change the values of the case in the `branches_sorted_by` method for the values it receives in the `params[:sort]` that are: `nil`, `'name'`, `'updated_desc'`, `'updated_asc'`.

Refactor spam validation to a concern that can be easily reused and improve legibility in `SpamCheckService`

NotesHelper#note_editable? and ProjectTeam#human_max_access currently
take about 16% of the load time of an issue page. This MR preloads
the maximum access level of users for all notes in issues and merge
requests with several queries instead of one per user and caches
the result in RequestStore.

A release's tag reference is just the name of the tag, not the entire
tag object.

This also fixes the tags index if a tag's message contains non-UTF8 byte
sequences.

* Registered video MIME types
* Currently supporting browser-supported formats with extensions that match the mime type

Remove builds settings from project settings; add builds settings route; add new controller action; put badge stuff under builds settings controller action

Manual actions are accessible from:
- Pipelines
- Builds
- Environments
- Deployments