issue #167: add Zone to the model
issue #167: add Provider.supportsDuplicateZoneNames, make apis implement iterator, enforce rrset methods need to take a unique zoneIdOrName; update naming conventions
issue #167: add zone id to the list output of the cli; support either zone id or name as --zone option
issue #167: port clouddns to support Zone; update naming conventions
issue #167: port dynect to support Zone; update naming conventions
issue #167: port route53 to support Zone; update naming conventions
issue #167: port ultradns to support Zone; update naming conventions