States, reactions and terrain

Phase 6 of #147. 17 states with stacks and ticks; the ten reactions (Electrocute, Freeze, Steam, Conflagration, Shatter, Toxic Burst, Hemorrhage, Execute window, Holy Fire, Wildfire); water soaks, oil and wood burn (#66).

Done when two players can set up and trigger every reaction; wooden palisades burn and can be put out.