Bug 1062798 - Replace custom JSON loaders with LazyLoader.getJSON in Settings App

Replaces custom JSON loaders with the LazyLoader.getJSON helper.
Replaced code in the app permissions, display, help, search and sound panels.
Also replaced within the APN utils module.
I just realized that although `xhr.open` takes an array as the second parameter but it only accepts an array with only one element or it fails. I would suggest to simply pass a string to avoid the potential confusion.