Emoji tweaks.

- Remove the numeric emoji indexes from Emoji->emoji.
- Add Emoji->setEmojiEditorList().
Add proper doc comment to the Emoji class.
Make sure the autocomplete emoji are called as assets.
Emoji: Add function to check whether editor list is empty.
Merge branch 'feature/emoji' of git://github.com/vanilla/vanilla into feature/emoji

* 'feature/emoji' of git://github.com/vanilla/vanilla:
  Make sure the autocomplete emoji are called as assets.
Merge pull request #2051 from vanilla/feature/emoji

Emoji tweaks.