Fix #4420: Previous track in dynamic random mix
Merge pull request #4626 from ntrrgc/master

Fix #4420: Previous track in dynamic random mix
Add internet_service to SpotifySearchProvider so custom context menu is correctly shown on playlist items created from the global search
Also add internet_service method for other search providers which have a internet services.
Shouldn't change anything in practice, but better to have items correctly inserted as Internet items FWIW. And will avoid other "custom context menu not working" issues if one day we implement one for
these services.
Add Spotify tracks to Spotify playlists by drag and drop
Sort music brainz releases according to status
Remove podcast episode automatic deleter out of PodcastDownloader
Allows to download multiple podcasts at the same time