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/coverprovider.cpp

@@ -26,5 +26,5 @@
 #include "core/application.h"
 #include "coverprovider.h"
 
-CoverProvider::CoverProvider(const QString &name, const float &quality, const bool &fetchall, Application *app, QObject *parent)
-    : QObject(parent), app_(app),  name_(name), quality_(quality), fetchall_(fetchall) {}
+CoverProvider::CoverProvider(const QString &name, const float quality, const bool fetchall, const bool allow_missing_album, Application *app, QObject *parent)
+    : QObject(parent), app_(app),  name_(name), quality_(quality), fetchall_(fetchall), allow_missing_album_(allow_missing_album) {}