Upstream: https://secure.phabricator.com/T3638
users should be able to drag a user from CC to assigned or vice versa if there is already an assignee, and they are replaced with a CC, the assignee should be moved (added) to the CC list.
Upstream: https://secure.phabricator.com/T3638
users should be able to drag a user from CC to assigned or vice versa if there is already an assignee, and they are replaced with a CC, the assignee should be moved (added) to the CC list.