Added --changetree and --dump dom:post-changes options to parserTests

* I often want to run a selser test with a specific changetree applied
  to it. Finally, I scratched that itch. Not sure why it took me so
  long.

* Also added an additional dom dump option to dump the DOM post-changes
  for debugging purposes.

Change-Id: I4ab7a5ad9480a4aacdb3ad35a722f9a31dfc78f1