NEW_API: Unhide audio effect APIs.

This change unhides all public APIs for controling audio effects exposed
by the following classes:
- AudioEffect
- BassBoost
- EnvironmentalReverb
- Equalizer
- PresetReverb
- Virtualizer
- Visualizer

Also fixes several problems in javadoc.

Change-Id: I541ee4ad0232312ec720545737cbcdb8c9a82597