Add support in TTS for volume and panning control of the synth output

Add two new parameters that are used when synthesizing text and
 playing it back directly to control the volume and left-right
 panning of the output.
Panning is applied using a balance law, which is not energy-preserving
 but which doesn't lower the volume when not panning / panning to
 center (legacy behavior).

Reduced amount of logs, and removed spoken text.

In TextToSpeech.java: added convenience method to handle the setting
 of the cached synthesis parameters.

Change-Id: I235d3d3193283ccc1891e2065d43787e3f63304d