Allow admin user edit.

* Now you can change all parameters of all users.
* The credentials used in the GeoStore client are the same of the user logged.
* When you edit an user, the role it's loaded.
* You cannot change the role of the user logged. If you need it, you must create another admin user before and do it with this user.
Merge pull request #3 from alediator/user_edit_revision

Allow admin user edit.