Addition of Process class and Process Management to GameEngine.

GameEngine::pushMsg() renamed to GameEngine::sendMsg() to be consistent with other files.
GameEngine::addProcess() adds a process to the gameEngine's processList;
GameEngine::tick() nolonger ha static code to perform it's processes, it will now call the trigger for all processes that are ready to go.
GameEngine::getGameState() added to return the engine state.

Main program loop will now terminate when the GameState becomes SHUT_DOWN.

Process class added. Still untested, need a process to implement to perform testing.