Change Details

**Context**: https://lists.wikimedia.org/pipermail/wikitech-l/2015-May/081644.html Because the global user merge tool is going to be deployed (and, presumably, //used//) and WikiGrok stores IDs and names of the users submitting responses, we must update WikiGrok to support merging users. As @Legoktm's email suggests, this'll entail listening to one of the `UserMerge*` hooks so that WikiGrok can keep user information up to date. Also, WikiGrok should //definitely// be listening to the `DeleteAccount` hook too…