Username & password with a character only

[DragomirStefanaCatalina]

Starting point: http://dev.rohelp.ro/en/admin/auth/user/

Expected:
Create a new user consisting of an username & a password with at least couple of characters

Actual:
Able to create a new user consisting of an username & a password with a character only

[AlecsGherghel]

@catileptic this can be grouped with #236 since both refer to username validation for which we'd have to probably override django's user/group model a bit

[francisc-czobor]

On the dev environment the password validators are deactivated. That's why you can have a one-character password. It's not a problem on the production environment.

[francisc-czobor]

The Django User model doesn't have a min_length constraint. To change that one would have to overwrite the User model and that would vastly increase the complexity. Why is this desired?