Feature: Q&A

- moderation
- needed for large audience talks : part of the room "team" should allow/disallow specific questions from audience for big talks
- transfer from chat
- with crowdcast it was duty of moderator to periodically remind participants to ask in the Q&A not in the chat. If there could be an easy way to transfer a post/thread to Q&A -- would be an awesome feature

HOWTO:
- could may be organized as a part of the (mattermost) chat
- a dedicated Q&A "channel" for the room, so each room would have Chat and Q&A
- a thread per each Q
- emoticons to vote (but no way probably to sort)