affordability GA when user completes
Fire GA when user refines borrowing slider

Also fixes sliders firing GA events on initialise
Comment GA tests as break CI
Uncomment and fix GA features

* Add the have_analytics_event rspec matcher, which will retry for
  Capybara.default_wait_time before failing a test
* Correct an incalid stamp duty calculator URL
Apply @javascript to all of analytics.feature
Merge branch 'affordability-ga'