Change scrolly-checkbox style

Our user research showed some users found the checkboxes to be a bit of a fiddle on mobile and tablet, so we're making the touch area a bit bigger and adding a border to make it apparent where the touchable edges are.
Move inputs to inside labels

So that the whole thing is clickable, but the inputs inside the labels.
Merge pull request #129 from alphagov/clumsy-fingers

Clumsy fingers