refactor getTrackInfo()

(this is in preparation for supporting other cc source)

- split into two methods: getTrackCount() and getTrackInfo()

- move track info parcelling to NuPlayer

- parcel in the mime type of the subtitle format

Bug: 15470448
Change-Id: If00724d8c3a2b2319cb9c5f29d3fe76347bfe947
11 files changed