increase test coverage of taglibwriter
Summary: increase the test coverage by testing more mimetypes, and use some unicode characters
Test Plan: taglibwriter test pass
Reviewers: mgallien, bruns
Reviewed By: bruns
Subscribers: svuorela, kde-frameworks-devel, Baloo
Tags: Frameworks, Baloo
Differential Revision: https://phabricator.kde.org/D15704