Eliminate the concept of 'Recipients' (plural). There is now just
a 'Recipient', which contains an Address that is either an individual
or a group ID.
MMS groups now exist as part of the group database, just like push
groups.
// FREEBIE
If the contact doesn't have an image, render a color-coded
background and the first letter of the contact's name.
1) Don't display anything during recipient resolution.
2) Display a # icon in material gray for recipients with no name.
3) Display a material group icon in material gray for groups with
no avatar icon set.
Closes#3104
// FREEBIE
