Not autojoining Jitsi calls

[edemaine]

Yevhenii and I discussed a better standard behavior for Jitsi calls:

1. Don't autojoin Jitsi when opening Comingle or joining first room or someone opens a new Jitsi tab. Instead, present a button that says "Join Call", similar to Zoom calls. Auto-joining is confusing/jarring in this case, and can be a privacy breach.
2. If you move from one room with an active Jitsi call (we'll need to use the Jitsi API to detect this) to another room with a Jitsi call, autojoin that call. This is the one situation where we want autojoin (for easy navigation between rooms), and it's not surprising in this case because you were already in a call. (And similar to Preserve Jitsi state when going room to room #76)
3. If you hang up on a Jitsi call (via red button), detect this (again via API), and replace Jitsi content with the "Join Call" button. This will avoid sometimes annoying Jitsi ads.

Related: #58, #35, #76.