Bug 1096898 - [Usage] Make Usage app work in Mulet

Please correct me if I wrong, as I see CostControl uses html imports to lazy load panels content, in non-debug build these imports are embedded (wrapped in comment node) by ```webapp-optimize.js``` [1] during app package building stage. And CostControl strivtly depends on that [2]. 

When we build app with "DEBUG=1 make" ```webapp-optimize.js``` isn't used, so somebody should take care about embedding these html imports. For that purpose ```LazyLoader``` is used, if it sees that panel's content isn't loaded yet (true for DEBUG build) then if performs the same thing as ```webapp-optimize.js``` does [3].

Then only thing that I'm not sure about - is level of overhead of ```LazyLoader.load``` for non-debug build - looks like we shouldn't have any performance problems with it. But maybe @julienw knows more? 

[1] https://github.com/mozilla-b2g/gaia/blob/70216cf8e35a09a6b3303119f1046b938448814c/build/webapp-optimize.js#L175

[2] https://github.com/mozilla-b2g/gaia/blob/70216cf8e35a09a6b3303119f1046b938448814c/apps/costcontrol/js/view_manager.js#L122

[3] https://github.com/mozilla-b2g/gaia/blob/70216cf8e35a09a6b3303119f1046b938448814c/shared/js/lazy_loader.js#L46