More cleanup; pulled out song list column to its own class

sublime/ui/common/__init__.py

@@ -1,11 +1,13 @@
 from .album_with_songs import AlbumWithSongs
 from .edit_form_dialog import EditFormDialog
 from .icon_button import IconButton
+from .song_list_column import SongListColumn
 from .spinner_image import SpinnerImage
 
 __all__ = (
     'AlbumWithSongs',
     'EditFormDialog',
     'IconButton',
+    'SongListColumn',
     'SpinnerImage',
 )