UDP-Support: Final fixes, changes

Technical Description:
- UnknownClient is now abstract, UDPClient and TCPClient implement the
required logic to reduce clutter
- Object polling has been modified on the server to prevent race
conditions
- Fixed race condition bugs that caused packet duplication and packets
being lost
- Added InternalPacket5Hello, which is sent 3 times on UDP to establish
the connection
- Added UnknownExceptionHandler to help with server crash debugging and
recovery.
- Removed debug code
- Server chat tests now pass on UDP