Maintain emoji line-height in it's context to avoid cut-off,
(Windows 10) http://i.imgur.com/xmdOLgv.png

This also allows us to get rid of the small bodge for the cut-off in
Safari

 - gl_emoji for falling back to image/css-sprite when the browser
   doesn't support an emoji
 - Markdown rendering (Banzai filter)
 - Autocomplete
 - Award emoji menu
    - Perceived perf
    - Immediate response because we now build client-side
 - Update `digests.json` generation in gemojione rake task to be more
   useful and  include `unicodeVersion`

MR: !9437

See issues

 - #26371
 - #27250
 - #22474

It now shows the line will be commenting on my highlight the line number cells with a lighter color. The button has also been made smaller, it was previously way over the top & took over a lot more space than it should of done

Closes #27543

Fix https://gitlab.com/gitlab-org/gitlab-ce/issues/25989

Fixed regression of note-headline-light where it was always placed on 2 lines, even on wide viewports

Fix text overflow in comments in MR

Adds MR ID to CHANGELOG entry

removes unnecessary changelog entry

makes toggle commit list and compare link as secondary

removes unnecessary function call