Found yet another bug in chapter processing (during merges). Changed merge behavior to favor incoming object structure. Refactored base class merge to not rely on __dict__

Fixed subtle property accessor bug in Gcisbase class stemming from excessive cleverness creating attributes and properties on subclasses.
Added assertions to test suite

Refactored date handling in Dataset from __init__ to properties to make handling available throughout object lifecycle; added test cases for same

Added support for new fields and smarter merges to datasets.  Added support for globally omitted fields to domain objects