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/CMakeLists.txt

@@ -254,6 +254,7 @@ set(SOURCES
   dialogs/errordialog.cpp
   dialogs/edittagdialog.cpp
   dialogs/trackselectiondialog.cpp
+  dialogs/addstreamdialog.cpp
 
   widgets/autoexpandingtreeview.cpp
   widgets/busyindicator.cpp
@@ -439,6 +440,7 @@ set(HEADERS
   dialogs/console.h
   dialogs/edittagdialog.h
   dialogs/trackselectiondialog.h
+  dialogs/addstreamdialog.h
 
   widgets/autoexpandingtreeview.h
   widgets/busyindicator.h
@@ -537,6 +539,7 @@ set(UI
   dialogs/console.ui
   dialogs/edittagdialog.ui
   dialogs/trackselectiondialog.ui
+  dialogs/addstreamdialog.ui
 
   widgets/trackslider.ui
   widgets/osdpretty.ui