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. 
I just noticed that we never actually emit `peerOpenedChannel` or `peerClosedChannel`. Let's remove and make these a TODO, or implement them.