Add support for hidden networks in networks.json/tbwifisetup

[joerick]

To support hidden wifi networks, a parameter scan_ssid=1 is needed in the wpa_supplicant.conf. We should change tbwifisetup so that it can translate this:

{
    "ssid": "My Wifi network",
    "passphrase": "hunter2",
    "hidden": true
}

into this wifi network configuration

network={
    ssid="My Wifi network"
    psk="hunter2"
    scan_ssid=1
}