Update MediaControlView2Impl

This CL does the following 5 things:

1) REMOVE setPrevNextListener API
2) REMOVE show/hideSubtitle API
3) EXPOSE Command related strings as public
4) CHANGE time parameter in show(timeout) from integer to long
5) CHANGE setButtonVisibility(visible) parameter from boolean to int

All changes are based on API review.

Test: build
Change-Id: If10a1849487fedf019383d2ab9cc2adc64df0608