[bug 985491] Use product string in generic form

* rewires everything so that the product picker shows up if you go to
  /feedback-dev/
* once you pick a product, it goes to /feedback-dev/<product> which
  now uses the product's display name in the form rather than "Firefox"
  hard-coded
* you can go back to the product picker if you have picked the wrong
  product or ended up there by mistake

r?