Updates to sound trigger test app.

Now supports loading model information from .properties files inside the
app's data directory. This lets you prepare models for your actual
device, rather than just fake data. If no .properties files are present,
falls back to the default fake three models.

Also adds support for playing some trigger audio, so you can use the
same device to (hopefully) have a trigger be detected.

Change-Id: I003849eb11d4995534d4c070838810d4519991f8