Currently this works by loading the HAML partials via XHR. While this is
not the nicest setup it _is_ the easiest setup using the tools we
currently have.

Loading this data asynchronously doesn't make loading the related
MRs/branches itself faster, it merely ensures that loading the issue
itself is not slowed down.

Fixes gitlab-org/gitlab-ce#14949

Add user avatar to user selection

According to endbosses' suggestions.

1. Make the "subscribed" text in Issuable sidebar reflect the labels
   subscription status

2. Current user mut be logged-in to toggle issue/MR/label subscription

Closes #9014

The only difference with #9014 is that I thoughed the author should also be
able to assign the issue. If this is unwanted behavior Ill revert it.

- Add label description
- Show label row when filtering issues or merge requests by label

Thanks @rspeicher.

Fix subtitles on minimize.
Fix styles for show.

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

Safari 9.0 does not yet honor the HTML5 `origin-when-cross-origin` mode,
and it's possible load balancers/proxies strip the HTTP_REFERER from
the request header. In these cases, default to some default path.

Closes #3122

Closes https://github.com/gitlabhq/gitlabhq/issues/9731

This ensures we don't end up running N+1 queries for the objects in the
affected collections.