Added AUTH/REGISTER messages, registration stuff

Added in AUTH and REGISTER message types. Got the hooks on the server
for both of them done. Got the client handling it. If an unknown user
logs in they'll be prompted to register. Known users are prompted to
authenticate and enter a password. THERE IS NO PASSWORD SECURITY!
Passwords are all handled in plain text! Passwords are all saved in
plain text! System isn't enforcing any rules yet. Just makes sure users
are authenticated.