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/context/contextview.h

@@ -91,7 +91,7 @@ class ContextView : public QWidget {
   void Stopped();
   void Error();
   void SongChanged(const Song &song);
-  void AlbumCoverLoaded(const Song &song, const QUrl &cover_url, const QImage &image);
+  void AlbumCoverLoaded(const Song &song, const QImage &image);
   void FadeStopFinished();
   void UpdateLyrics(const quint64 id, const QString &provider, const QString &lyrics);
 
@@ -164,6 +164,7 @@ class ContextView : public QWidget {
   Song song_playing_;
   Song song_prev_;
   QImage image_original_;
+  bool lyrics_tried_;
   qint64 lyrics_id_;
   QString lyrics_;
   QString title_fmt_;