Fix reserialization of mw-data.body.html

This bug caused all references containing complex content (e.g. links
or templates) to be dirty-DOMed and reformatted by Parsoid.

ve.dm.MWReferenceNode.js:
* Parse the original body.html and check if it's semantically equal to
  the new value. If so, don't set it.

ve.dm.Converter.js:
* .normalize() the converter output to remove empty text nodes and
  merge adjacent text nodes

ve.dm.example.js:
* Update reused reference test to have body.html absent, not empty
* Add a link to one of the reference tests so this bug is triggered
** The link's attributes are ordered specifically so that toDomElements
   will reorder them, at least in Chrome (may behave differently in
   other browsers)
** This test fails without this fix in place

Change-Id: Idc091a14422fbb117a3d06fc6bb9497768086fc3
Merge "Fix reserialization of mw-data.body.html"