Prevent error with partially created user data

Previously if an error happened during couch user submission the
existence of a django user trail would cause a 500
Cleanup
Show spinner when creating mobile users

This prevents multiple quick submissions and is a little nice since
callcenter accounts will have the lovely xml case submission delay.
Use proper method of getting a django user

Oops!
Merge pull request #614 from dimagi/mobile-user-bug

Mobile user creation bug fix