compose_box: Replace compose box with a banner in DMs with deactivated users#816

gnprice merged 3 commits intozulip:mainzulip/zulip-flutter:mainfrom

sm-sayedi:issue-675-dms-with-deactivated-userssm-sayedi/zulip-flutter:issue-675-dms-with-deactivated-usersCopy head branch name to clipboard