Core/SmartAI: Implement SMART_ACTION_SET_POWER, SMART_ACTION_ADD_POWER and SMART_ACTION_REMOVE_POWER (param1 = powertype, param2 = newPower). Required for upcoming EAI to SAI conversion (for ACTION_T_SET_UNIT_FIELD) (only SMART_ACTION_SET_POWER is required for the conversion but might as well do it right when on it).