delete groups

Whoops, forgot to add this functionality earlier.

- allow owner to delete a group
- change all group lists to closed curation with group=False when group deleted

bookwyrm/urls.py

@@ -258,6 +258,7 @@ urlpatterns = [
     re_path(
         r"^group/(?P<group_id>\d+)(.json)?/?$", views.Group.as_view(), name="group"
     ),
+    re_path(r"^group/delete/(?P<group_id>\d+)/?$", views.delete_group, name="delete-group"),
     re_path(
         r"^group/(?P<group_id>\d+)/add-users/?$",
         views.FindUsers.as_view(),