Implement UX for displaying message threads in private groups
Depends on #650 (closed). Subtask of #127 (closed).
May depend on fixes for #443 (closed), #525, #526 (closed), #527 (closed), #552 (closed).
Depends on #650 (closed). Subtask of #127 (closed).
May depend on fixes for #443 (closed), #525, #526 (closed), #527 (closed), #552 (closed).