Support for FlaggedRevs patrolling 

NOTE THAT I DID NOT TRY EVEN COMPILING THIS CODE, MUCH LESS RUNNING IT. But I'm pretty sure it's correct. ;)

Replaces basic built-in MediaWiki patrolling. Will always only review at the most basic "accuracy level", which is what every Wikimedia wiki uses. 

Added 'ActionReview' to 'enum Action' to support FlaggedRevs API queries.

Added config option 'PatrollingFlaggedRevs' / 'patrolling-flaggedrevs' to enable this feature, false by default.