Archmage mode and powerup indicator

Added a couple new features:

A new "Archmage Quest" mode is available from the "New Game" menu. This generates a random episode similar to "Random Quest", except that that the parameters are tweaked to make it quite a bit harder. You also start with the green staff.

And there is now an icon to tell you whether there's a powerup crystal in the current level, so you can be sure to find it before exiting.