TIF: Add content rating systems

- Change the strings for translation to English only.
- Add content rating systems for many countries.
- Update javadoc of TvContentRating which is auto-generated based on
  tv_content_rating_systems.xml and strings.xml

Bug: 16862855, Bug: 16889743
Change-Id: Ifd81c85934b8631e8ae00633639989275982ecfb

Author: Sungsoo Lim