Add AuthorizedWidgySite which checks user for permissions

The following API views now check permissions:

-  ContentView.put checks change permission
-  NodeView.post checks add permission
-  NodeView.put checks change permission
-  NodeView.delete checks delete permission
-  ShelfView.get filters results based on add permission
-  NodeTemplatesView.get checks change permission
Added UnsafeHtml Widget.

This Widget is unsafe because it provides a potential for permission
escalation.  No non-superuser should have the following permissions:

-  page_builder.add_unsafehtml
-  page_builder.change_unsafehtml
-  page_builder.delete_unsafehtml