added a key to jump to a song in the media library

This commit introduces a new key to bind, key_go_to_media_library. It
will switch to the media library and select the song under the cursor.

src/settings.h

@@ -117,6 +117,7 @@ struct ncmpcpp_keys
 	int SavePlaylist[2];
 	int GoToNowPlaying[2];
 	int GoToContainingDir[2];
+	int GoToMediaLibrary[2];
 	int ToggleAutoCenter[2];
 	int ToggleDisplayMode[2];
 	int ToggleInterface[2];