Improve album cover loader, lyrics search and streaming support

- Improve album cover loader
- Add album cover loader result struct
- Move album cover thumbnail scaling to album cover loader
- Make init art manual look for album cover images in song directory
- Make album cover search work for songs outside of collection and
  streams
- Make album cover search work based on artist + title if album is not
  present
- Update art manual in playlist for local files, devices and CDDA
- Make lyrics search work for streams
- Add stream dialog to menu
- Remove dead code in InternetSearchModel
- Simplify code in InternetSearchView

src/collection/collectionplaylistitem.h

@@ -46,6 +46,8 @@ class CollectionPlaylistItem : public PlaylistItem {
 
   bool IsLocalCollectionItem() const { return true; }
 
+  void SetArtManual(const QUrl &cover_url);
+
  protected:
   QVariant DatabaseValue(DatabaseColumn column) const;
   Song DatabaseSongMetadata() const { return Song(Song::Source_Collection); }