End of Tuesday morning

I added player classes today, which will support hotseat multiplayer and play vs the AI.

AI is not yet implemented.

There's several tutorial screens in, and a flag that turns off the tutorial.

I track your running score, both within the level, and overall.

Next: a dialog at the end of the level to show players' scores, and a dialog at the end of the game to show the winner, and then I can focus on the main menu, the options screen, and other frippery.