For rows added by the SpecialStatsAddExtra hook, add an HTML id of "mw-" plus the message key

This will allow for the row to be easily selected via CSS, so extensions
can easily point the user at the relevant row(s).

Change-Id: Ib93e05d1ef89666ddcb132b5eb4b620b160b5565
Merge "For rows added by the SpecialStatsAddExtra hook, add an HTML id of "mw-" plus the message key"