Jobqueue migration htmlcacheupdate

RFCR @nmonterroso 

There are a few files with references to `HTMLCacheUpdate` that I don't think get loaded anywhere, but I'd like to confirm with @Wikia/platform-team before asserting that.

extensions/WikiScripts
extensions/FlaggedRevs
extensions/Scripting
extensions/BadImage

Also, maintenance/wikia/restoreOn.php : The MultiRestore task doesn't actually work (even without any changes), so it didn't make sense to try updating it (especially if this is going to be deprecated because the only access point is via a link in Special:TaskManager to undo a Special:Multidelete task)

Lastly, the reason Damon's changes appear in this PR is that I based my branch off of his to try to debug some SQL nonsense that was really a result of me forgetting to set `wikiId` on a task.
Since this lives in includes/wikia/tasks/Tasks, this will be available in Special:Tasks. Is that intended?