Improved selser test generation for lists and tables

* For lists and tables, this patch attempts to add a new listitem
  or a td/th cell rather than insert text/comments which could be
  buggy in the list context. The old code was generating edited
  DOMs like <ol>text</ol> which is not valid.

* Regenerated blacklist.
  - 1 passing selser test
  - But a number of previously blacklisted selser tests now have
    their outputs modified.

Change-Id: I9f45f668111c84aa2dd78016acec182310796a16