Move scripts to bottom of HTML

This enables better page performance: http://developer.yahoo.com/blogs/ydn/high-performance-sites-rule-6-move-scripts-bottom-7200.html
No need to defer scripts included at bottom of document.
Merge branch 'master' into move-scripts

Conflicts:
	_includes/_head.assets.html
Remove erroneous custom variable call
Remove analytics.js as this is included in application.js
Remove code as is included in application.js
Merge pull request #144 from alphagov/move-scripts

Move scripts to bottom of HTML