Using the sed script from
https://gitlab.com/gitlab-org/gitlab-ce/issues/59758

Group milestones can only be referred to by name, not IID. They also do not
support cross-project references.

 - 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

Handle videos in:
- MD preview in notes: commit, issue/MR, MR diff
- New notes in: commit, issue/MR, MR diff
- Persisted notes in: commit, issue/MR, MR diff

Signed-off-by: Rémy Coutable <remy@rymai.me>

This reverts commit 3e991230.

# Conflicts:
#	app/models/project.rb

Using the syntax proposed in #13829 [project_reference]%(milestone_id | milestone_name)
to get a link to the referred milestone.

Also adds the ability to run rspecs with relative_url_defined on the enviornment. For example:

RELATIVE_URL_ROOT=/gitlab rspec

Closes #1728