feat(llc): Added participants count in CallState

[Brazol]

Overview

Handlers for the call.session_participant_count_updated event.
The Coordinator will occasionally deliver this event to all clients, and it will carry the most recent state of:

anonymous_participant_count and participant_count_by_role

Implementation notes

watch parameter is now added to Call.get() and Call.getOrCreate() methods. When set to true the coordinator events will be listened to even before joining the call.

The CallState is extended with participantCount and anonymousParticipantCount fields.
This values from the call.session_participant_count_updated event are used to update those fields but only when the call status isn't JOINED. Once the call is JOINED, these values will be populated from the SFU heart checks.

[deven98]

LGTM