[bug 999089] Firefox desktop product dashboard

* add infrastructure for product dashboards
* add prototype generic product dashboard for products that don't have
  their own dashboard
* add prototype Firefox desktop dashboard

This is all prototype-quality code! The purpose here is to get a feel
for how we're visualizing the information and not for good programming
or maintainability--that'll come later.

There are also no tests since we're still prototyping things and getting
a feel for what we want to do.