Add admin undelete endpoint + frontend #144
Description
The admin log frontend already has filtering. Also, nobody (not even supers) can see content OR activity for deleted content, so now we need:
- An endpoint that allows super users to restore deleted content, which should just call the RestoreRevision DbWriter function with the second to last revision
- Add buttons to the adminlog that let you undelete content (each admin log has a type and a contentId, use the type to show the button, pass the contentId to the endpoint)