Disable TTS "Listen to the example" if not supported

If current TTS locale (most of the cases same as device locale) is
not supported by the TTS engine, field for setting synthesis speed
and "Listen to the example" will be disabled.

Added new field, "Default language status" to indicate level of support
for currently selected language. It can take one of three messages:
%s is fully supported
%s requires network connection
%s is not supported
Where %s is locale display name.

Added example string that will provide a fallback for example text
if not provided by Settings or TTS engine.

Change-Id: Ia2a920a71197a85d3812fc8df9dfed4ebe6b515f
Bug: 9982002