RTCPeerConnectionStats is missing state stats (connection, ice, gathering, signaling)

[henbos]

RTCPeerConnectionStats does not contain PC state information.

• If we fix #483 we have iceState on a per-transport basis. Would it make sense to compute iceConnectionState and expose it on the PC level?
• Should we also expose connectionState?
• Should we expose iceGatheringState?
• Should we expose signalingState?

[fippo]

but you can, inside the context of the getStats response access the peerconnection and all those attributes?

[henbos]

I think we can defer to the APIs rather than getStats for this