Add mousetrap for keyboard shortcuts
Create a go to mapping modal

* When pressing “g m” a modal appears asking for an old URL, entering
the URL will take you directly to that mappings edit screen
* “g m” for “go to mapping”
* Uses the existing find_global method to resolve a mapping without site
Fix failing hits test

* There were two “Old URL” fields and the assertion was looking at the
wrong one
* Instead look for “Old URLs”
Merge pull request #253 from alphagov/go-to-pages

Create a go to mapping modal