Modified the logic behind the user update, to allow the admins change the user's password without providing the current password.

refs #1410
Test added for user's controller.

refs #1410
Modified the password change logic to admins. Now they don't need to use the current password to change his password.

Realized more acceptance tests when an admin try to change his password or a user password.

refs #1410
Small usability improvements when changing passwords

Better strings, ask for the current password before the new password.
Also added more tests for UsersController.

refs #1410
Merge pull request #57 from mconf/Feature1410

Allow admins to set a user's password

refs #1410