Load picturefill polyfill via jspm
New optimisied versions of the index cover image
Use new responsive image srcset syntax for homepage hero image
Add simple routing to app.js to prevent js errors on other pages
Revert "Add simple routing to app.js to prevent js errors on other pages"

This reverts commit fe31b44f4394b6abaefdc7c1c18c55f716625973.
Add simple routing to app.js to prevent js errors on other pages
Merge pull request #35 from guardian/ph-js-routing

JS routing. Fixes #12
Add base image
Merge pull request #34 from guardian/picture

Use <picture> for homepage cover image
Merge branch 'master' into lanyrd-events