tweaked/idealized uproxypeerconnection interface

Tweaked the uproxypeerconnection interface so my work on socks-rtc compiles and updated samples to match.

TESTED: grunt and ran `src/coreproviders/samples/freedomchat-chromeapp/` manually, messages still flow, no console errors. 
So, I chose `fromPeerData` only to match the name in `PeerConnection`. If you think this reads better here, do you also think it would also read better there?