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.
1) When sending an SMS or MMS to multiple recipients, only show one
ConversationItem, but provide statistics on the number of recipients
delivered to.
2) Still break up the messages for secure and insecure messages.
