The "contact" option in the attachments tray now brings you through an
optimized contact sharing flow, allowing you to select specific fields
to share. The contact is then presented as a special message type,
allowing you to interact with the card to add the contact to your system
contacts, invite them to signal, initiate a signal message, etc.
Previously, we were always rendering images as squares. Instead of doing
that, we now render them as close to true-to-size as possible (within
reasonable min/max width/height boundaries).