adding skeleton code for python client
Adding ICE and SDP infrastructure

we have ICEAgent and SDPHelper in webrtc.py client, classes
that implement helper functionality

ICE implementation after https://tools.ietf.org/html/rfc5245
STUN Agent implementation

The implementation of the STUN agent, both in client and server
modes. We follow rfc5389 with minimal implementation of SOFTWARE
and MAPPED-ADDRESS attributes.
wip: ice