WIP: fix bug 436405: MetaData isn't updated while there is not metadata at all
Trying to fix https://bugs.kde.org/show_bug.cgi?id=436405
Contains two fixes:
- entry doesn't get inserted into tracks table when the track's metadata doesn't contain title. Fix: use track's name as title
- lyric doesn't get updated when the lyric is empty. Fix: update empty lyric but don't insert lyric entry to TrackMetaDataModel
Known issue:
- tracks that don't have metadata on playlist is marked invalid on second load (add it to playlist and exit then re-open, track is invalid)
- on fallback, using track file name as metadata's title isn't technically correct