Disable unavailable notification checkboxes

Updates usage of HTMLCheckMatrix to match recent refactor allowing
options to be forced on or off.  Instead of hiding unavailable
checkboxes now we show them greyed out and unchangable. Depends on
https://gerrit.wikimedia.org/r/#/c/61163/ in core.
Bug: 47743

Change-Id: I9284a2ad29de654062e54a78a76c10dd49c35ed7
Merge "Disable unavailable notification checkboxes"