Hide Advanced Config Page settings until the device has a serial number

[cocarrig]

To prevent confusion on initial client setup process, it is beneficial to not show the ability to input a private URL. The private URL field is sometimes input in error by clients at the initial setup time, which will result in a failure to register the device appropriately.

Enhancement: when loading the configuration page, on a device with a serial that is unset, hide the advanced configuration section of the setup page.

[cocarrig]

Closing this in favor of approach in #90