Globally disable delete_selected action in Admin. Fixes #221

this removes the drop down selection widget!

NOTE: we could add a button in template's `object-tools` block
but that will not be able to handle multiple selection. Also the
checkboxes for multiple selection are not rendered when
delete_selected is disabled. For reference see:
sehmaschine/django-grappelli#839

If the user wants to delete an object they will have to open each
object in a separate page and delete it from there!

tcms/core/admin.py

@@ -37,3 +37,8 @@ class KiwiUserAdmin(UserAdmin):
 # user admin extended functionality
 admin.site.unregister(User)
 admin.site.register(User, KiwiUserAdmin)
+
+# globally disable the 'Delete selected' action
+# see https://github.com/kiwitcms/Kiwi/issues/221 and
+# https://docs.djangoproject.com/en/2.0/ref/contrib/admin/actions/#disabling-actions
+admin.site.disable_action('delete_selected')