Not receiving heartbeats with StreamingSubscriptionConnection

[dconnelly]

The code seems to expect a heartbeat response every 45s but I'm not seeing any, at least while connected to Office365. This causes the underlying http connection to time out before lifetime minutes is reached, unless I've made sure that ExchangeService has a much larger timeout than would be applicable to other requests.

A simple fix would be to set the http request timeout to lifetime minutes just for the hanging GetStreamingEvents call.