UDP Packets

IpCommunication now has everything called "packets" instead of
"messages" to make it easier to tell the ChatTwo protocol's messages
from the packets that are sent.

Also added more comments to the IpCommunication class.

Also moved PacketTransmissionEventArgs to the IpCommunication class.
Still not super happy about UdpCommunication.SendMessage being an event
triggered method, but I don't know of a better way to do it right now.