Add version attribute in tv_content_rating_system.xml

- 'version' attribute is added in 'rating-system-definitions' tag.
- Update javadoc for the format change of XML file in TvContentRating.
- Fix some errors in the javadoc comment.

Bug: 16805703
Change-Id: If9473c89cef0777232470d67f1542a5e5eac3182