Do proper HTML preservation in ve.dm.MWReferenceListNode

Store the HTML as a domElements array like everywhere else, rather than
as a string. Also disable HTML attribute preservation because there's
no point doing that when we're already preserving all of the HTML.

Also fixed a misnamed attribute (<li li="foo"> --> <li id="foo">) in
the test case.

Change-Id: I36bf8bade8118e07a75eb6f3a2427a00ef4915d7