Fix ModelRegistry bugs

* In matchTypeRegExps(), skip string types
** Didn't break because we currently have mixes of strings and regexes
* Combine types from rel, typeof and property rather than picking one
** Added test case in ve.dm.example that resembles actual Parsoid output
* If the element has extension-specific types, not only restrict type
  matching to extension-specific types, but also require that *all* types
  present on the element be matched

Change-Id: Iacf3851a0ca9081d2c813b42435484a47cec6230
Merge "Fix ModelRegistry bugs"