SoundTrigger API improvements.

This CL implements the SoundTrigger API improvements as given in b/22860713. Only the java-level
parts are implemented in this CL.

Key changes include:

* Addition of a SoundTriggerManager/SoundTriggerDetector system API to manage
  the sound-trigger based sound models.
* Addition of a SoundTriggerService service that manages all sound models
  including voice (keyphrase) and sound-trigger based models.
* Includes logic to write sound-trigger based models to the database.
* VoiceInteractionManager service now uses SoundTriggerService instead of
  SoundTriggerHelper.

Bug: 22860713
Change-Id: I7b5c0ed80702527c4460372efeb5e542d3693a69