Problems Sovled!

Mostly at least. It is now possible to create users, and even login!
There is no logout yet though.

Only problem that remain is if a login attempt fail. See
ChatTwo_Server_Protocol's MessageTransmissionHandler method for details.

Shared Files:
- ChatTwo_Protocol has gotten a public constand for the
DefaultSharedSecret. Easier when it is only located one place.
- Fixed a mistake in thinking that UserID was a byte. It is an int32!
- Removed Password from UserObj.

Server app:
- Now throws an exception if it receive a message and the database
connection is not activated.
- DatabaseCommunication now also returns the username of a user with a
successful login attempt.
- DatabaseCommunication now returns false rather than throw an exception
when a user already exist with that name.
- Removed some unused variables.
- Added socket to OnUserStatusChangeEventArgs, now to fond out how to
use it.
- Added a new login error, 0x02, for "User is already online". But
user's aren't removed from the _users list when they go offline, this
need fixing.
- Made the NotifyIcon not vanish anymore.
- NotifyIcon now has the correct name.