Future-proofing WelcomePacket

WelcomePacket now stores welcome message, and will include it as
received if re-transmitted
DifficultyPacket update

Corrected type value, added GameType, fixed difficulty property not
getting set
Don't ignore terminators on object list packets

The object list packets include a terminator 0x00 int at the end of the
list that wasn't getting read; this caused ArtClientLib to complain that
the packets weren't completely read
Added PausePacket
Added data console as possible client
Some documentation fixes
ThreadedArtemisNetworkInterface improvements

Queue is thread-safe; fixed problem with server-to-client packets not
getting taken from queue; some cleanup (be careful not to send packets
to the server before WelcomePacket is received)