Extract animation out into methods

So that it will be easier to implement different behaviour for small
screen devices.
Tidy small screen spacing and remove mobile JS

Tightened the spacing so that the edges of the text are following the
standard guttering on mobile.

Remove mobile specific JavaScript as adding JavaScript to the mobile
view doesn't aid in giving the user context as to where they have gone
where the animation on desktop would.
Use Function.prototype.bind over $.proxy

Now we have a polyfill for bind in the frontend toolkit use bind rather
than proxy for forcing a `this` on method calls.
Merge pull request #33 from alphagov/mobile-animation

Tidy up mobile browse and JS tidying