Menu error when webform-enabling content types

The Webform Default Fields module correctly sets up default field nodes for content types that are webform-enabled at the moment when the Webform Default Fields module is installed, but it fails to clear the menu cache and therefore does not display the "Default Webform Fields" menu item when editing a content type if you webform-enable it after Webform Default Fields has already been installed. To fix this, I've added a submit handler function which correctly does the setup whenever someone submits changes to the webform admin settings form.

Also, when uninstalling Webform Default Fields, it fails to delete default field nodes for content types that were webform-enabled but have subsequently been webform-disabled. I've therefore modified the hook_uninstall function so it correctly removes those nodes.

I'm attaching a patch with my changes.