Add a button to SettingsApp that lounches the PP, and a back button to PP main screen

https://github.com/mozilla-b2g/gaia/blob/master/apps/settings/js/developer.js Sample code that launches the First Time Use app from the settings. What should be done: 1. Implement a button in Settings App and connect the js file like the one above that launches the PP. 2. Implement a back button in PP, and connect the js file that looks like one above but launches settings.

Button in Settings App and js file were added. Back button in PP and js file were added. At the moment back button is always displayed. Finally the button should be displayed only, when PP is opened from Settings App.

I know it's a hack, but in theory we could use the settings db to indicate when the PP is launched from settings. Here's how: 0. The settings app creates/sets a settings db key-value-pair like: privacy_panel.launched_from = settings. 1. The privacy panel app always checks for and clears the privacy_panel.launched_from settings db value when it starts up. 2. If the settings db value is "settings" then the back button is shown. Otherwise, it is hidden. The end result is that the back button will be shown whenever the settings app launches the privacy panel. if the privacy panel is launched from the home screen the settings db key-value-pair will not be set and the back button won't be shown.