we should not be setting the user_id of new links unless we're sure this is the first time the link has been added to a thread.
get participants of a thread.
add participants_names method
only validate uniqueness of comment cothread_id if link association is defined.
return full data for participants in json, not just names.
assign thread participants to backbone relation.
add getParticipants() method to thread model.
render participants to a thread in the statbar.
style avatar in popover so that it comes out looking vertically aligned on the same line.
move logic for popover title/content to renderPopover method and separate getStatusMessageText method.
add basic check in cucumber feature that participant avatar appears in statbar.
add todo note.
resolve conflict.