MusicImport: fix switching of the metadata editor to metadata only mode
MusicImport: update the importing of albumart to work with storage groups

Both directory and embedded images should now be imported properly.
MythMusic: start updating the edit metadata screen to work with storage groups
HLS: Don't allow duplicate streams to be created.

If an identical one exists we return the ID/details for that instead.
HandleMusicFindAlbumArt: only save the filename not the full path
findIcon: add option to ignore the cached filename
EditMetadata: update the internet image search to work with storage groups

Note: bumps the ABI version so core and plugins need to be recompiled
Merge remote-tracking branch 'upstream/master'