This fixes the remainder of the GitPushService specs.

This ensures the right caches are flushed when adding a branch via the
UI, instead of only flushing this one random cache.

This ensures Repository#add_tag calls Repository#before_push_tag instead
of just 1 random cache expiration method.

This ensures that Repository#rm_branch calls
before_remove_branch/after_remove_branch instead of just 1 random cache
expiration method.

The methods used for this are Repository#tag_count and
Repository#branch_count which cache their output in Redis as well as
memoizing it in an instance variable. Both methods have a corresponding
methods/hooks to flush the caches at the right time.

removes automatic setting of main_language to project for it to set a main language you have now to make a commit to the project

We've got all these polymorphic type-checking methods, might as well use
'em everywhere it makes sense.

Added in Mar 2014. Only usage removed in Sep 2014.

This was removed from the interface in
https://github.com/gitlabhq/gitlabhq/pull/6027 but its implementation
lingered around for two years.

This method was duplicating default Rails behavior.

This method was added in Dec 2012, its single use was removed two days
later, and it's been there ever since.

* Add Labels tab to Groups
* Add decorator for label so it's aware of Milestones.

With this change we avoid doing N+1 queries when viewing Milestone's
Issues/MRs from a Group context.

Make methods return ActiveRecord Relations instead of Arrays.

Closes #13663

When rendering 1 commit takes over 5ms (on my laptop: around 9ms), it
saves seconds in rendering time to show 100 instead of 500 commits.

Button full width on phone on MR/issue.