admins appeared

Now some users can be admins. Only these users can access
usrs resource (others could maybe still see user details in a
different controller) and edit them. Admins can also make admins
via usrs controller.

If other users can edit their own data, that would be in a different
controller, possibly modified view from Devise.

It works fine actally.

Signed-off-by: Zeljko <zeljko@zwr.fi>
remove class that is not needed

Signed-off-by: Zeljko <zeljko@zwr.fi>
do not allow sign up

Users cannot sign up in this app, only admin can create user accounts.
However, once in the system, users can edit end even delete own

Signed-off-by: Zeljko <zeljko@zwr.fi>