Status instead of Avatar

Since avatars aren't supported on the server-side at all, I hid the
avatar column and added a status column instead.
More Comments

Added a few comments and popup massages to make the prototype easier to
understand.
- Small comment to explain the DialogResult from the FormLogin and
FormRegister.
- New popup on startup to show the configured ServerAddress. Mostly for
prototype debug use.
- Made the "UdpClient started on port x" popup only show up on debug
mode.
- Few more comments around the ServerAddress defining area.