Support resuming games and starting games from arbitrary positions

[lightvector]

The following are similar and would be nice to have:

• Resumption of games interrupted by the server going down (currently the game do get logged to the database move by move, so they will be there, and will show up in historical games as a game with no winner and an end condition of "adjourned").
• Creation of games beginning in arbitrary (but legal as far as piece count and defense of pieces on traps) starting positions. Both specifiable directly via a setup-like string, and specifiable by reference to the position of a particular other game on a particular turn.