Add some custom JSON serializers

- datetime.datetime:

    This serializes to isoformat

- uuid.UUID

    This serializes to a stock standard string
Add new Domain schema
Add a to_appstruct function to Domain model

This allows a quick way to get an appstruct version of the model after
it has been retrieved from the database
Add full schema validation

This gets called after the individual SchemaNodes have been validated,
and is used to verify more than one field at once.
Return array of domains

Of course, get the appstruct from the Domain model, and append it to the
list.
Add save method for adding new domains