Fix country selector bug

When selecting Wales or Scotland or Northern Ireland, it was selecting all of the England checkboxes as well.

Thanks to @jackfranklin for javascript WIN
England selector has special cases.

Needed to include London and Yorkshire in the regex match, which wouldn't get picked up just with filter on indexOf('England').
Rewrite using a ternary
Don't toggle, use value of country checkbox

This fixes a bug if SE England checkbox was already selected and then you checked England, it would toggle SE England off.
Merge pull request #40 from alphagov/country_selector

Country selector