Define remote config file spec and add remote config feature

[matt-cook]

Allow centralized management of multiple devices, push notifications to send command and update settings centrally. Would also function as a work-around for #14

Likely will use GCM: https://developer.chrome.com/apps/cloudMessaging

[rkralston]

This web server looks interesting:

https://github.com/kzahel/web-server-chrome

[matt-cook]

@rkralston we're looking at using this solution for #9. This specific feature will be implemented by defining a spec (likely REST/JSON based) for remote config files and adding a field in the Kiosk admin to specify and arbitrary remote server.

Not GCM as previously suggested.

[matt-cook]

Editing this feature to simple remote config spec, full management website will be an instance of Westminster: https://github.com/zebradog/westminster and beyond the scope of this app.

[matt-cook]

This will be handled via policy files instead of remote config: https://github.com/zebradog/kiosk/issues/37