[bug 851733] Helpfulness chart on kb and l10n dashaboards.

It turns out we already had this chart on the kb dashboard but a CSS selector in the js was broken and it wasn't rendering. I fixed that and added a chart to the l10n dashboard as well. And the KPI dashboard chart is now showing data for votes across all locales instead of en-US only.

I'll file a followup to convert this to RickShaw.

r?