TvContract: Address the feedback from the API review

This change addresses the following comments from the council:
- Provider authority should be "android.media.tv"
- Rename COLUMN_DATA to COLUMN_INTERNAL_PROVIDER_DATA and add comment to
  indicate data is internal to the provider that inserted it, and should
  not be decoded by other apps. It would be nice to restrict read access
  to this column, but not essential.
- Hide COLUMN_LOCKED since implementation isn't defined yet, also
  questions about how it interacts with Unicorn.
- Fix typo in ORIGINAL_NETWORK documentation.
- All provider MIME types need to be changed to follow platform
  conventions: "vnd.android.cursor.dir/channel",
  "vnd.android.cursor.dir/program", etc. (Notice singular tense and no
  package prefixes since they're part of the platform API.)
- Rename Programs.COLUMN_DATA to COLUMN_INTERNAL_PROVIDER_DATA, along
  with docs update, for the same reasons as above.
- Rename COLUMN_DESCRIPTION to COLUMN_SHORT_DESCRIPTION and update docs
  to indicate it's a recommended maximum length, not a hard cap.
- COLUMN_GENRE should be split into two columns: COLUMN_BROADCAST_GENRE
  (from broadcast standard) and COLUMN_CANONICAL_GENRE (from an Android
  standard). Define a subclass with the Android canonical genres, which
  are simple strings that are comma-separated when inserted into
  COLUMN_CANONICAL_GENRE.

Bug: 15345342
Change-Id: I7f8e70aef617475a59d096fd73a551e7df8a1d3a