Implement a better network detection scheme


Turns out that there is no consistent way to check for network connectivity using the v1 gadget APIs.  Therefore, we do it manually by trying to contact the server every ten seconds.  We could implement a lighterweight "Ping()" WebMethod in our service to facilitate this, but since checking for an update is something we need to do and it is rather light anwyay, we'll just constantly do an update check when the gadget is visible (i.e. the user can see it).  If the gadget is not visible, then we back off completely.