Separated MongoDb callback code into Datastore module so Adapter can primarily use promises.  Needs a bit of cleanup.
Merge commit '56af2fa363d823bee87a08934630ae33ce198e83'

Conflicts:
	lib/adapter.js
Some clean up; removed a couple dead modules checked in for historical reasons; removed callback parameters in adapter push/pull since not tested -- can re-add if needed.