Wifi menu status

New feature to add an icon to the menu to show Wifi status. The Wifi icon shows as greyed out if Wifi is not available. You can touch the icon to prompt to switch Wifi on/off as appropriate.

Small change to NetworkMgr:getWifiStatus() to ping gateway rather than 8.8.8.8, as wifi may be connected with no Internet access!
But the icon status has been set when the menu was updated by getWifiStatus(), so using it again when you tap it would be two calls to NetworkMgr in quick succession. It would only not be accurate if you opened the menu then waited for a while (in which time the Wifi was dropped), then you tapped...