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.
1) We now delay MMS notifications until a payload is received,
or there's an error downloading the payload. This makes
group messages more consistent.
2) All "text" parts of an MMS are combined into a second text
record, which is stored in the MMS row directly rather than
as a distinct part. This allows for immediate text loading,
which means there's no chance a ConversationItem will resize.
To do this, we need to include MMS in the big DB migration
that's already staged for this application update. It's also
an "application-level" migration, because we need the MasterSecret
to do it.
3) On conversation display, all image-based parts now have their
thumbnails loaded asynchronously. This allows for smooth-scrolling.
The thumbnails are also scaled more accurately.
