base

Added APIs for audio preprocessing

Added APIs to control pre processes applied on captured audio.
Those APIs are still hidden until reviewed by API council.

Three types of standard pre processes are supported:
- Automatic Gain Control (AGC) by AutomaticGainControl class
- Acoustic Echo Cancellation (AEC) by AcousticEchoCanceler class
- Noise Suppression (NS) by NoiseSuppressor class

A method is added to AudioEffect class to query audio pre processings
applied by default by the platform on a given AudioRecord session ID.

Change-Id: I0b9fceeb8c704dd06319c3b52b85c96fe871d51d