Divided controllers in many small controllers

- Added view and edit controllers. Code from single controller was
divided in three.
(I still need to decided a better implementation since because the code
became a little messy).
- UserController now allows to update an existing user.
- The header, where the edition of users used to be, now is in a
different view. There's no really a *good* reason to let the user see
everything in one single view.