WIP: Selser v3

* Some bug fixes in DOMDiff.

* Changes to DOMDiff to propagate modified flags up ancestors to
  root and add modified markers to every subtree that has some
  descendent modified. Used different modification flags on nodes
  depending on the type of modification detected.
  - inserted, deleted, child-deleted, modified, subtree-changed
  Serialization doesn't look at the specific flag itself, just
  that a flag exists, but the flag type might be useful for other
  applications like blame maps, diff display, etc.

* Incorporated selser-mode into serializeNode and emitSepAndOutput
  functions -- no other changes required.

* Deleted DiffToSelserConverter.

* Improved robustness of emitSeparator against missing DSR which
  eliminates the 'dsr backwards' error warnings seen previously.

* 9971 (up from 8261) selser tests passing
  249 (up from 178) failing non-selser tests pass in selser mode
  19 (down from 1658) failing selser tests pass in non-selser mode

Change-Id: Ib2ce9953d79cc859b292571ce0371cb7f35771f9
Merge "WIP: Selser v3"