Bug 1100964 - Expose a wipe button from developer menu. r=?

https://bugzilla.mozilla.org/show_bug.cgi?id=1100964
Recently we've added `DialogService` to setting app and you could the following code fragment to prompt a confirmation:
```
require(['modules/dialog_service'], (DialogService) => {
  DialogService.confirm(...);
});
```

Please check this file[1] for details.

[1]: https://github.com/mozilla-b2g/gaia/blob/master/apps/settings/js/modules/dialog_service.js