Stations: Expose "show" attribute to the mobile app

Arduino inverts this flag and interprets it as “disabled” instead of
“connected”. This adds support for the disable attribute into the
change_stations function which just inverts the value back.
Mobile App: Fix device detection

Using all protected JSON broke my automatic device scanning/detection (uses /jo to get fwv and see if valid).

I have added a /jv which only shows the firmware, something that's shown on the home page anyways. 

This should be enough to fix my feature without compromising security.

Thanks!
Use limited options JSON reply when unauthenticated
Use helpers.py check_login
Merge pull request #20 from salbahra/master

Stations: Expose "show" attribute to the mobile app