bug 43191 tag edits from GS in RecentChanges

Hook into RecentChange_save (like AbuseFilter and MobileFrontend) and check openTask cookie
maintained by E3Experiments openTask.js; if an edittitle is in cookie as a
gettingstarted task then call ChangeTags::addTags().
Also hook ListDefinedTags so the right things show up in Special:Tags.

This patch works for me.

Change-Id: Ifc1fd8968fba23d9f3fe048a60e4721734d9c933