Bug 1033549: [CostControl] Add a per-app data usage list

https://bugzilla.mozilla.org/show_bug.cgi?id=1033549
When the promise, hide the sync path, move the check inside `loadApps()` method and make it looking like:
```javascript
Common.loadApps()
  .then(finishInit)
  .catch(function(reason) { debug(error); finishInit(); });
```