First shot on custom user management (#1)

Ref: https://github.com/ideas-box/ideasbox.lan/issues/1
I'm not sure about this. I think we should return by default the more common case, and I think this will be saved user (with fk and so on). For example when we will be testing the blog, the library, etc., we always have to deal with fk, so with saved objects. What do you think?