Display embedded cover images
Summary:
introduce EmbeddedCoverageImageProvider to get access to embedded covers
store the fact that tracks have an embedded cover image in database
when importing files, check and store the presence of embedded cover
makes MusicAlbum and MusicAudioTrack use the embedded cover images
BUG: 380442
Test Plan: embedded covers are shown. albums without a cover but with tracks havong embedded cover are now showing a nice cover
Tags: Elisa
Differential Revision: https://phabricator.kde.org/D17163