Use mediawiki.api.watch for watching/unwatching pages

Also fix action=watch and action=unwatch, and use tokens when creating
links to them (see r88522 and r89545)

Bug: 45329
Change-Id: I3659ae24decdd82723d78e9b9862068f59f660d0
Merge "Use mediawiki.api.watch for watching/unwatching pages"