UntilServerDoUsApart - implementing logic for starting WebSocket transpo...

...rt on WindowsPhone 8.1.

Note that the CI needs to be updated to be able to build Store product/test projects after they took dependencies on Windows.Networking. I ran FunctionalTests on my machine and they passed. I also have a WP8.1 chat client I tested that the change works E2E (i.e. that the client can connect to the server and receive messages).