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

https://bugzilla.mozilla.org/show_bug.cgi?id=1033549
Part of the confusion probably stems from the result. `appManifestURL` is only available for requests made with a specific `appManifestURL`, so I'm essentially copying all samples when a request was made globally.

I agree however that the model reconcilation that's happening in the view needs to be moved, so I'll do that.