Review Session: Improve join message and hide when there is no current sync

Currently we often get clients asking what they should do with the sync popup when we’re just sharing a review playlist for them to look at in their own time, this confuses them. I would suggest all review playlists do NOT have syncing on by default, unless some one on the top right clicks START SYNC, which then will notify people if there’s a sync active or not when they open the playlist. This would mean we can just share playlists to people and they’ll be able to find their way more intuitively without thinking there’s some one presenting which they do not know about.