Move scripts to the bottom of the page

Script tags should be the last thing on the page for performance related
reasons. We should also send as few scripts as possible.

To that end I have:

- Moved the application and analytic scripts to the bottom of the page.
- Meged the application and analytics code so its a single download.
- Moved the print detection analytics code into a JS file and included
  it with the analytics code
Let JS apear optionally in the head

This will enable us to transition applications over to the JS at the
bottom approach rather than forcing it upon everyone.
Merge pull request #193 from alphagov/scripts-at-the-end

Move scripts to the bottom of the page