First shot on custom user management (#1)

Ref: https://github.com/ideas-box/ideasbox.lan/issues/1
Yes. We need to create account for people that will never log in, and doesn't what a password is, and it can used for, etc.
So users may login (for now, only the staff; a bit later, only power users), but the majority of the users will never, and we don't want to ask a password to people that doesn't know what it is.
If we decide to have a password mandatory for user account creation, the risk is that we'll only have dummy password.
For sure, then, only users with a non null password will be able to log in (let me add a test case for this :)).
Does that make sense? :)