Reconcile IronPigeon.Relay web api differences

[AArnott]

The relay has been totally re-implemented since the v0.5 version. Are the web APIs exactly the same? If not, what can we learn from the differences? Which ones should be reverted?

• AddressBookController is missing.
• PrivacyController is missing.
• InboxController push notifications
• InboxController long poll
• Periodic expired blob/mailbox purging - Tracked by Add periodic blob/table deletion #43