Having a list or number of people currently connected

[ungb]

Would be good to have a list of number of people currently connected.
You can also just count the cursors you see to get this number.

For example, Maybe I'm expecting to walk through code or a document with 6 people, Having the number of people connected can give me a sense of knowledge that everyone I'm expecting is here and connected. If that number drops I know someone left.

/cc @simurai This looks related to #22

[jasonrudolph]

👍 Once we ship authentication, we'll have the building blocks in place to provide a list of portal participants. xref: https://github.slack.com/archives/C65B6TS0K/p1503323703000443

[jasonrudolph]

Now that the popover UI is in place, you can see the list of people participating in your portal. 😅