implement reading of rating tag
Summary: Allow to read the rating stored in the metadata for idv2, vorbis and ape tags. Since the value ranges all differ, translate them to a range from 0-10 like we use for xattr ratings
Reviewers: mgallien, michaelh
Reviewed By: mgallien
Subscribers: cgilles, kde-frameworks-devel, Baloo, bruns
Tags: Frameworks, Baloo
Differential Revision: https://phabricator.kde.org/D12156