Enforce a .json extension (in DEV mode only).

Also changed the only example I found of it not doing so.

This is needed by some changes I am making to the routing.
image profiles for imager.js
Adding imager
styling of image container
use container strategy
add connection speed class to body
Merge branch 'master' of github.com:guardian/frontend into the-json

Conflicts:
	dev-build/app/Global.scala
Update comment to reflect changes
concat imager.js
fixing popular images
fixed wide popular
Escape card title html correctly
Merge pull request #2143 from guardian/the-json

Enforce a .json extension (in DEV mode only).
made wrapper for imager.js
no delay; using
adding `dns-prefetch` link
Merge pull request #2157 from guardian/win-phone-bug

Use Imager.js for our responsive image solution
fix jshint
Merge pull request #2160 from guardian/win-phone-bug

fix jshint
Merge branch 'master' into commercial-travel-component

Conflicts:
	common/app/assets/javascripts/bootstraps/common.js