Re-structure messages to use unions (again). Non-POD can be stored outside the union.
Handle add/remove effect chain messages in EngineEffectsManager.
Add a set-parameters request for EngineEffectChain and handle it.
Add EffectRequest processing/dispatch loop.
Add tracking of active EngineEffects to EngineEffectsManager.
Add CLEAR_STRUCT macro for clearing the structs.
Remove CHAIN_SLOT message types.
Add SET_EFFECT_PARAMETER message for setting an effect parameter's values.