Description of problem:

The participants list is supposed to show users who are currently logged into the workspace, but logged out users seem to hang around in the list forever.

Version-Release number of selected component (if applicable):
1.4.5

How reproducible:
Seen at least twice.

Steps to Reproduce:
1. First user logs into the workspace
2. Second user logs into the same workspace
3. Second user leaves the workspace

Actual results:
Both users are visible in Participants

Expected results:
Only first user should be visible

Additional info:

We need to consider explicit "Leave workspace", explicit sign out, closing the browser tab, and session timeout.  Any one of these should remove a user from the workspace, and thus from the participants list.