Cast API overhaul (#173)

Re-write the shim<->bridge messaging interface and session creation/update handling for better accuracy.

ext/src/senders/mirroring.ts

@@ -162,10 +162,10 @@ function receiverListener(availability: string) {
 
     if (availability === cast.ReceiverAvailability.AVAILABLE) {
         wasSessionRequested = true;
-        cast._requestSession(
+        /*cast._requestSession(
                 selectedReceiver
               , onRequestSessionSuccess
-              , onRequestSessionError);
+              , onRequestSessionError);*/
     }
 }