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/internet/internetplaylistitem.h

@@ -36,10 +36,11 @@ class InternetPlaylistItem : public PlaylistItem {
 
  public:
   explicit InternetPlaylistItem(const Song::Source &type);
-  InternetPlaylistItem(InternetService *service, const Song &metadata);
+  explicit InternetPlaylistItem(InternetService *service, const Song &metadata);
   bool InitFromQuery(const SqlRow &query);
   Song Metadata() const;
   QUrl Url() const;
+  void SetArtManual(const QUrl &cover_url);
 
  protected:
   QVariant DatabaseValue(DatabaseColumn) const;