add key_select_album: select album around cursor

Default key for this is 'B'. This use to be the default for
ToggleBitrateVisibility, which has changed to '#'.

src/settings.h

@@ -118,6 +118,7 @@ struct NcmpcppKeys
 	int Lyrics[2];
 	int ReverseSelection[2];
 	int DeselectAll[2];
+	int SelectAlbum[2];
 	int AddSelected[2];
 	int Clear[2];
 	int Crop[2];