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 delayed the done() call till the promise was resolved because otherwise the tests can run before `FindMyDevice.init()` is finished. The previous loadJSON mock made the callback init synchronous so it wasn't an issue, but not we're returning a promise in the mock.
Maybe this would be better if `init()` returned a promise that was resolved when it finished executing.