Implement support for writing rating information for taglib writer

Summary:
Add support for writing the rating tag to all
supported mime types. Since the implementations quite
differ, implement mime type specific paths when necessary.

Test Plan: tests pass

Reviewers: bruns, mgallien

Reviewed By: bruns

Subscribers: kde-frameworks-devel, Baloo

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D18604