User sending via UDP

1. Sending Objects via TCP don’t want to work, so MMUser objects will
be send as a String via UDP now.
2. UDP Messages now need a Prefix like CONNECT:<The Message>,
MESSAGE:<The Message>
Network changes

1. Improved the getMyLanAddress-Methode
2. Added some new Network-Testcases
3. Removed TCP-Functionality
4. Improved some other network stuff