Clean up MozL10n API use in Cost Control #1057795

This is relating bug 1057795
It's best to move the conversation about naming schemes to mozilla.tools.l10n :)

Wrt. CostControl, I believe we can deal with it. I prefer setL10nAttributes because it's closer to the bones (similarly to how Node.classList.add('class') is not named Node.styleWith('class');), but I guess we'll manage to keep the separation between mozL10n.localize and CostControl's Common.localize :)


gauravmittal - per app owner's request, please, revert Common.setL10nAttributes to Common.localize and use the wrapper instead of direct calls to mozL10n.setAttributes (but do not alter DOM's Node.setAttribute).
Apologies for doubling your work on that!