Fully migrate MediaStates management to reactivity (#27, #47)

[evdokimovs]

Part of #27

Required for #167

Synopsis

Currently intentions of the Senders/Receivers will be sent by Room object, but it will be more correct if Command::UpdateTracks will be sent on State updates.

Also in this PR, disable/mute before call will be more correctly implemented. Now Command::UpdateTrack will be sent after Event::PeerCreated, but before negotiation start.

Solution

Migrate MediaState management of Sender/Receiver to the reactivity.

Send Command::UpdateTracks based on constraints before negotiation start.

Checklist

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