Handle typing of html/head/body in live HTML
* Fixed various issues with starting from an empty document
* Made it so we generate an insert if the root element is new
* On the browser side, treat an elementInsert for html/head/body specially
  and just add the id and attributes to the existing implied node
Merge branch 'dangoor/4736-delete-across-tags' into adobe-nj/implied-tag-fixes