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
9d2d26af2e