* Excited groups care about reactions.
Adds reacting var for open turfs. Reacting gets set to the return of react() inside the open turf's process_cell() proc.
Adds turf_reactions var for excited groups. turf_reactions gets set to the result of has_reactions OR reacting. Excited group processing will check if the excited group's has_reactions is REACTING or STOP_REACTIONS before dismantling the excited group. Excited group processing will set the excited group's has_reactions to NONE at the end before MC_TICK_CHECK.
Fixes water vapour not consuming water vapour when temperature is below WATER_VAPOR_DEPOSITION_POINT.
Changes water vapour reaction to have a consumed var, it gets set to MOLES_GAS_VISIBLE when it freezes a turf or makes it slippery. If consumed, then water vapour moles decrease by consumed, set reaction results and set return value to REACTING.
Fixes water_vapour reaction by making its mole count decrease by consumed instead of attempting to do arithmetic on the water vapour list, which somehow didn't runtime.