Closes #29971

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/29192

See https://gitlab.slack.com/archives/frontend/p1488973548024005

 - 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

This adds the 2016 emoji as well as support for using SVG images instead of PNGs.

It also fixes a number of incorrectly categorized emoji and other minor issues.

Upgrade Rake task for Gemojione 3.0.0 and generate sprites.

Upgrade aliases.json by pulling down index.json from the gemojione repository and running the generate_aliases.rb file.

Changelog: https://github.com/jonathanwiesel/gemojione/blob/master/CHANGELOG.md#v301-2016-07-16

For the specific emoji added to the Unicode standard, see: http://emojione.com/releases/2.2.4/

Huge kudos to Jonathan Wiesel (@jonathanwiesel) for his work on the gemojione gem!

No reason to split it into a separate gem when the gem barely did anything. We can use gemojione directly, making updating gemojione that much easier.

Also fix the Rake task and update gemojione to 2.6.1. This adds the EmojiOne Spring update.

Changelog: https://github.com/jonathanwiesel/gemojione/blob/master/CHANGELOG.md

By pre-calculating the digests we can manually construct the emoji URLs,
removing the need for using Rails' asset URL helpers. The reason we
don't want to use these helpers for Emojis is two-fold:

1. Rails' image_url() method is slow, really slow. For one it _might_
   have to calculate digests but it also performs a lot of other
   intensive operations (judging by the source code and based on
   measuring timings).

2. We have a lot of Emoji which coupled with the above can result in it
   taking minutes to load Emoji autocomplete data.

Using this pre-calculation setup generating the digests takes around 7
seconds (including the time it takes to start Rails/Rake), and only
around 600 milliseconds to load _all_ the autocomplete data of a project
(measured locally).

This commit _does_ change the Emoji URLs from absolute to relative URLs
as these are much easier to generate.

To update the Emoji data simply run:

    rake gemojione:digests

Then commit any changes.

Fixes gitlab-org/gitlab-ce#14009

Also adds a script to re-generate them from the index.

Current as of Gemojione 2.2.1 - https://git.io/vgQx0