Tags, sentiment and the leaderboard no longer wait on the database

What shipped

• Automatic tags and sentiment appear right after a question is sent. They are worked out on our live service instead of waiting for the database, and a question is only analysed once however many servers see it.
• The Q&A leaderboard is built from the live room. The venue screen and the host's analytics read it from the live service, refreshed every few seconds, with names hidden when the event is anonymous.
• Moderators' tag changes reach phones at once and are saved to the database a moment later.
• Past events keep their results. An event that ended before this change still shows the totals saved in the database.