Update Users API to handle role objects or ids
Update Users API to handle role objects or ids

Closes #3357
- API method User#edit now handles User objects that have either
  an array of Role ids or objects.
- Fixed error handler notification on upload modal controller.

dbalders/Ghost-Admin,acburdine/Ghost-Admin,TryGhost/Ghost-Admin,JohnONolan/Ghost-Admin,TryGhost/Ghost-Admin,acburdine/Ghost-Admin,airycanon/Ghost-Admin,kevinansfield/Ghost-Admin,airycanon/Ghost-Admin,dbalders/Ghost-Admin,JohnONolan/Ghost-Admin,kevinansfield/Ghost-Admin