#150 More robust group / user management

[mikael kasurinen]

Need make more use of groups.

I should be able to restrict users from going to a
certain newbb forum by their group. For instance there
would be a forum A which is only accessible to Group A
and so on. Also granting post access one by one is
pretty cumbersome. You should be able to simply choose
everybody from a simple list or just give post access
to a whole group by a single click.

Also ranks should be a thing that could be assigned to
a certain group. Doing everything by hand is a pain in
the ass.