Prevent players with invalid characters on their name from joining servers

Tweaked some stuff to prevent users with invalid characters on their name from joining DMP servers

and I also added an Enum for handshake replies. I had to add the regex
because Windows wouldn't throw if the username had ", <, > or |.
Replaced int handshake response checks with HandshakeReply enum

Replaced the message of client version to display the first 7 bits
instead of the whole hash.
Added a check for usernames that contains / or \ to stop messing up servers
Close the process after the Goodbye message

This way I can make my auto updater addon work.