Wrap changes lists in <div class="mw-changeslist" />

This affects Watchlist, RecentChanges and RecentChangesLinked.

A <div class="mw-changeslist-empty" /> is already used on all of these
when the list isn't generated (somewhat inconsistently coded, though).

Bug: 8844
Change-Id: I1ab2a54e22f318713c2211d63b29c184751a3589
Merge "Wrap changes lists in <div class="mw-changeslist" />"