ExpAI: Encourage forward advancement when capturing villages
ExpAI: capture villages with injured units if no enemy can reach
ExpAI: ignore unreachable enemy leaders when selecting keep
ExpAI: capture more villages if we can't recruit any more this turn
ExpAI: fix the name= value of Place Healers CA

It doesn't really matter for anything in practice, but should be done
right.
ExpAI: add retreating and village hunting CAs