[bug 969667] Merge desktop and mobile forms

* create new generic form that merges desktop and mobile forms
* move around instructions so important instructions come before the
  fields they apply to--this is better for privacy-related information
* add pushstate support so going back and forth in the form works with
  form controls and browser controls
* this doesn't support jumping into the middle of the form
* rework infrastructure so it's possible to add additional cards and
  measure drop-off rates
* makes this structurally like the firefox os feedback form so all forms
  now have a similar structure

This looks a little worse on Desktop, though. This form could definitely
use better strings and better design, but that's out of the scope of
this change and would require a lot more work.
[bug 969667] Replace mobile/desktop forms with generic

* nixes desktop and mobile form routing (yay!)
* replaces that with new generic form
* update tests to denote that we now essentially ignore validation
  errors with email addresses and descriptions--Thanks!
* update ancient android form post handling to also ignore errors
* clean up code after all that
[bug 969667] Clean up CSS/JS

This cleans up some of the CSS and JS after removing the desktop and
mobile feedback forms.