Fix teardown of live extension nodes

* Separate teardown into (insertOrUpdate|remove)Node
* Override insertOrUpdate completely to avoid generating
  extra transactions. Surface#applyStaging creates all the
  transactions we need.
* Override remove to popStaging before calling parent.
* Fix isEmpty check to use getInnerValue (ignoring whitepsace)

Change-Id: I903302af178d6f923de00aff9c58e5330d682813