Updated Messages

Added HelloMessage.java and made changes to all of the other messages,
adding a PRIORITY field and relevant getter method to them.
Added R2D2Connection

This class is used as a wrapper for a socket, allowing you to easily
send and receive Message objects through that socket. This class can be
used on both the client and server sides once a socket is established.
First draft of R2D2GameController

Created an untested but theoretically complete draft of
R2D2GameController.