Added debug view at bottom of each page.

The debug view will only show if the user preference dev-debug is set to true.

Currently only shows the time the page was rendered (to help debug caching issues).
Made JsHint happy
Merge branch 'master' of github.com:guardian/frontend into debug
Change state by adding an active class
Remove redundant localStorage check
Merge pull request #606 from guardian/debug

Added a debug block at the bottom of each page - based on a user preference