Feature request: Show a count of how many people have joined

[douglasnaphas]

As a retro participant in the retro lobby, I want to see how many people have joined my retro So that I don't have to count the icons of participants showing up in the bottom of the lobby.

Acceptance Criteria:

• [ ] A count of participants who have joined shows up in the retro lobby

[vanderhoop]

@douglasnaphas hmmm... this is a reasonable and sensible ask. let me think on the design aspects