Bug 1093534 - [Stingray][Settings] add settings list to settings app

I noticed that when we enter one of the `SettingsList`, that is to say, the `activePanel` becomes instance of `SettingsList`. There will be no `confirmSelection` method for `activePanel` to invoke. Because there is no implementation of `confirmSelection` on the prototype chain of `SettingsList`. 
And we'll get error like this
```
JavaScript error: app://settings.gaiamobile.org/js/settings.js, line 70: TypeError: this.activePanel.confirmSelection is not a function
```