Implementing custom emojis
Following design exploration at https://gitlab.com/gitlab-org/gitlab-ce/issues/13931#note_85978465
### Problem
Custom emoji give a sense of community. Make custom emoji possible as a way to let communication be more expressable by multiple people.
### Additional notes
Groups are up first, individual projects are considered later, personal namespaces are out of the question. See for more information https://gitlab.com/gitlab-org/gitlab-ce/issues/13931#note_86312705
### Plan of action
__MVP custom emoji:__
- https://gitlab.com/gitlab-org/gitlab-ce/issues/48907
- https://gitlab.com/gitlab-org/gitlab-ce/issues/27977
- https://gitlab.com/gitlab-org/gitlab-ce/issues/24212
Future:
- https://gitlab.com/gitlab-org/gitlab-ce/issues/31596
- https://gitlab.com/gitlab-org/gitlab-ce/issues/48908
- https://gitlab.com/gitlab-org/gitlab-ce/issues/48911
<img src="https://gitlab.com/gitlab-org/gitlab-ce/uploads/0c759226399a42d1e107008067bca8dd/Artboard_4.png"/>
epic