Fixes for saving and loading different playlist file formats
Add more tests to verify success of playlist saving by reloading the file and comparing some contents. Test that non-ASCII path names don't get broken right away.
Fix non-ASCII path names breaking in XSPF playlists
BUG: 435779
Small fixes to m3u saving and loading. Change ASX mimetype to better working one. Avoid writing unnecessary xml tags in ASX, which improves compatibility with at least VLC + avoid writing tags multiple times in some special cases (tests, at least).