Add ng-textcomplete

[Refs #72499946]

Added ng-textcomplete directive and js file.
Add ability to reference users

[Refs #72499946]

Changed the inputs a bit (they’re now generated in Textcomplete
directive), fixed strange behavior when directive is called before data
is available.
Update Users API

[Refs #72499946]
Added following_handles action to get handles of all users that we’re
following, added test, updated routes.
Merge pull request #30 from Design-Collective/ft/user-reference-user-72499946

Ft/user reference user 72499946