Use ramping gain when processing EffectChains.

* Ramp changes in wet/dry gain.
* Ramp-in and ramp-out when the chain becomes enabled or disabled on a per-group basis.
* Add in-place optimization for when we are fully-wet and fully-dry with no ramping.
Load sane default values for EngineEffectParameter from the manifest.
Fix goofy initialization order requirements for EffectChains by making them send all their existing state right after being added to the engine.
Change SEND mode processing to not double the signal when fully dry.
Add virtual destructor to EffectInstantiator.
Add DISALLOW_COPY_AND_ASSIGN to EngineEffectChain.