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!
Is it really necessary to probe wifi status on each menu update? The `NetworkMgr:getWifiStatus` will be called on nearly every tap on the menu including switching menu tab and going to sub menu and returning to parent menu.