Use Select2 input for user selection in the admin
Use Select2 Input for the Admin Interface whenever seelecting a user.
The advantage of the Select2 is that you can search and that it loads the users asynchronously,
so you don't need to load the list of all users anymore.
Create new objects of the above mentioned Models.
Notice the select2 field.
Try some autocompletion
Reviewed By: WyldBot
Maniphest Tasks: T369
Differential Revision: https://phabricator.wildfyre.net/D248