Update toolkit version so it pulls it from our own gem repo
Add missing external-link image files
Remove external-link images
Enable copying of assets

Include a new version of the toolkit with the sass correctly looking in
the right folder for the external images. Update the copy assets method
to copy assets to the right folder and create a folder for them if they
aren't within the main images folder.
Remove gem.fury with fury
Move images into stylesheets folder
Merge pull request #52 from alphagov/update-toolkit-version

Update toolkit version and add missing image files