and add the ability to record the fulfillment time

* Make currency a property of the Order (for validation purposes)
* Remove null=True from Char fields
* Use InheritanceManager for subclassing OrderItem
* Change VerifiedCertificate to better handle some new use cases
* Cleaned out old migrations
* Tests!

when in a dev environment.

Feature/vik/oe ui

ErrorDescriptors do not have xml_attributes field

Enable mongodb to be used as back-end for git-based authoring workflow