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

https://bugzilla.mozilla.org/show_bug.cgi?id=1033549
Yeah, when I did this I wondered if it might make sense to use two progress segments on the app progress bar to represent the wifi and mobile data, with each segment being colored the same as the legend.

Otherwise, I'm worried about the confusion of having two types of data usage toggle and only showing one in the app usage list..