TTS Connection callbacks are called on main thread.

After experimenting with the new TTS API I found out that receiving
ConnectionCallbacks#onEngineStatusChange and #onServiceDisconnected
callbacks on non-main thread are problematic. They are very rare and
overhead of dealing with them in separate thread is high - in most
cases user just wants to process those callbacks in the main thread
context. This change should make new API usage easier.

+ Fixed default values of speech speed in voices from v1->v2 wrapper.

Change-Id: I76d3b607b3b931b7eb10aa180775fd3607c43bd9