Enhance F10 debug menu functions

[KevinHake]

Some nice to haves (that might just become separate issues):

• Select units to place from a big menu containing buildpics (could even be a breakout window) instead of typing unit codenames in text
• Make it easier to see where a new unit will be placed
• Ability to add/delete map features?
• Unit deletion?
• Change of active player? (not sure if this is really simple or really infeasible)