Ability to query number of users in a room within the Popular Rooms API

[dizzket]

It would be very useful to be able to, when generating the list of popular rooms, attach some kind of user count. For each associated room entry there would be a property, "usercount" that would display the number of people broadcasting in partymode from within that room.

This could be done clientside, but it would require that the popular rooms API and the partymode API both share the same rooms. If we add any sort of output limit to the partymode API then the two lists could fall out of sync, and comparisons between them would be impossible.