Code cleanup

* Remove dead constant, LAST_HANDLER
* Create new graphics constants.
Login handling

* New class to store Account data
* New class to store Character data
* Implemented response to login success from LOGIN
* Implemented state transition from logout success
Implemented sending messages

Implemented network service method to instruct the handler to write the
message to the channel.
Chat message handling

* Outline Game class to receive chat messages when in game
* GameClient handling of inbound chat messages
* Lobby handling of outbound messages
* Client sending and encoding outbound chat messages
Initial work on chat messages server-side.