Display lock icon in Express client to indicate leader building an agenda

Prior to this release, when a leader entered the App-based Agenda Builder, the leader was removed from the Attendees panel of the Express client. This was confusing for participants who had joined the event through the Express client, because it appeared as if the leader had exited the session.

With this release, when a leader launches the Agenda Builder in the Cornerstone Classroom App client, participants who have joined the session through the Express client can now see the presenter's name appear at the top of the Attendees panel with a 'lock' icon. This indicates to Express client participants that the leader is still in session, but is running the Agenda Builder.