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/core/mainwindow.ui

@@ -469,6 +469,7 @@
     </property>
     <addaction name="action_add_file"/>
     <addaction name="action_add_folder"/>
+    <addaction name="action_add_stream"/>
     <addaction name="separator"/>
     <addaction name="action_shuffle_mode"/>
     <addaction name="action_repeat_mode"/>
@@ -827,6 +828,11 @@
     <string>Rescan songs(s)</string>
    </property>
   </action>
+  <action name="action_add_stream">
+   <property name="text">
+    <string>Add stream...</string>
+   </property>
+  </action>
  </widget>
  <layoutdefault spacing="6" margin="11"/>
  <customwidgets>