woExecute onLoadLanguage in synthesis thread.

Previously, onLoadLanguage was executed without minding synthesis queue.
Now onLoadLanguage is queued item, so it won't be executed before the items
on the queue (previously TTS could receivecall to onLoadLanguage
while synthesizing in completly different language).

I've divided SpeechItem into ControlSpeechItem and UtteranceSpeechItem.
Utterance one dispatches callbacks about synthesis progress.

Bug: 7510063
Bug: 5351864
Change-Id: Ibd156b3cecb190e5c07c4451e61121127b54d51e