The admin form was supposed to prevent webhooks being created with an

events list that included the wildcard event and other events (because

they were covered by the wildcard event). However, the CSS selectors

used were incorrect. They have new been updated.
Additionally, the webhook API endpoint to reflect this. Any webhook

created through the API with the wildcard event will have its events

limited to the wildcard event. Unit tests have been added to reflect

this new behaviour.

Ran unit tests.
Manually verified the admin form worked.