Combined with the switch to server acked messages, this will
prevent the race condition that occurred when an incoming message
showed up at exactly the moment the app updated.
It'd be great if we could just do REPLACE INTO, but it's too
late to add a UNIQUE() constraint. =(
Fixes#2287Closes#3029
// FREEBIE
1) In addition to the Recipient interface, there is now
RecipientDevice. A Recipient can have multiple corresponding
RecipientDevices. All addressing is done to a Recipient, but
crypto sessions and transport delivery are done to
RecipientDevice.
2) The Push transport handles the discovery and session setup
of additional Recipient devices.
3) Some internal rejiggering of Groups.
1) Move the attachment structures into the encrypted message body.
2) Encrypt attachments with symmetric keys transmitted in the
encryptd attachment pointer structure.
3) Correctly handle asynchronous decryption and categorization of
encrypted push messages.
TODO: Correct notification process and network/interruption
retries.
