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. 
Last suggestion here: `signalForPeer` to match `signalForPeerQueue` (just like `dataFromPeer` and `dataFromPeerQueue`)?