First step of refactoring 'timedtext' code.

Goal
1. Removed dependency of TimedTextPlayer on AwsomePlayer.
2. Generalized TimedTextParser to TimedTextSource and its subclasses.

Summary
1. Introduced TimedTextDriver, TimedTextPlayer (new implementation),
TimedTextSource (and its subclasses).
2. Removed TimedTextParser.

Remaining TODOs
1. Revise VideoVidew, Gallery3D app, AwesomePlayer to check if
'pause' and 'resume' works well.
2. Consider revising MediaPlayer APIs such as setParameter() ->
addTextSource(). Need more thoughts.

Change-Id: Ie0c4f15b9690102de755cef6940f8c31ccf78e27