Create ref list insertion tool

Fixes (follows-up I1b48ef5240, I6daff5c596):
* Invalid html passed to jQuery constructor.
* Use prop() instead of attr() for boolean values.
* Use append() instead of html() when appending nodes instead
  of parsing html.
* Rename shadowed variable name clash 'mw' to 'mwData'.
* Fix odd construction where we parse '{}' to create an empty
  object.
* Have ve.ce.MWReferenceListNode#update perform changes off-document
  in a detached tree.
* Fix deep property access that can fail. mwData is set to
  either JSON parse of data-mw attr or empty object.
  Accessing mwData.attrs.group needs to be guarded by whether
  mw.attrs is indeed set.
* Have `mw` and `about` attribtue in references list roundtrip
  (especially mw which can data we aren't editing/re-creating).
* Add missing 'refGroup' property to MWReferenceListNode's
  data element (similar to what MWReferenceNode already has).

Change-Id: I67e4f378ccd04e97361d8e58ae57db5353075756
Merge "Create ref list insertion tool"