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/covermanager/albumcoverloaderresult.h

@@ -0,0 +1,52 @@
+/*
+ * Strawberry Music Player
+ * Copyright 2020, Jonas Kvinge <jonas@jkvinge.net>
+ *
+ * Strawberry is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Strawberry is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Strawberry.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef ALBUMCOVERLOADERRESULT_H
+#define ALBUMCOVERLOADERRESULT_H
+
+#include "config.h"
+
+#include <QImage>
+#include <QUrl>
+
+struct AlbumCoverLoaderResult {
+
+  enum Type {
+    Type_None,
+    Type_ManuallyUnset,
+    Type_Embedded,
+    Type_Automatic,
+    Type_Manual,
+    Type_Remote,
+  };
+
+  explicit AlbumCoverLoaderResult(const Type _type = Type_None, const QUrl &_cover_url = QUrl(), const QImage &_image_original = QImage(), const QImage &_image_scaled = QImage(), const QImage &_image_thumbnail = QImage(), const bool _updated = false) : type(_type), cover_url(_cover_url), image_original(_image_original), image_scaled(_image_scaled), image_thumbnail(_image_thumbnail), updated(_updated) {}
+
+  Type type;
+  QUrl cover_url;
+  QImage image_original;
+  QImage image_scaled;
+  QImage image_thumbnail;
+  bool updated;
+
+  QUrl temp_cover_url;
+
+};
+
+#endif  // ALBUMCOVERLOADERRESULT_H