Write EffectChain updates to the EngineEffectsManager.
Remove unused MessageType from EffectsResponse.
Add enabled/enabledForGroup tracking to EffectChain.
Handle ENABLE_EFFECT_CHAIN_FOR_GROUP/DISABLE_EFFECT_CHAIN_FOR_GROUP messages in EngineEffectChain.
Add mix accessor/setter in EffectChain.
Get rid of some old assumptions in EffectChainSlot.