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.
1) Change the MessageSender logic so that individual SMS messages
are encrypted whenever there is a secure session, unless the UI
explicitly specifies otherwise.
2) Change the MMS logic so that messages to a recipient with a
secure session are all sent individually, instead of including
those recipients into the batch plaintext message.
