remove unused icons
Merge branch 'master' of github.com:guardian/frontend into remove-unused-icons
Optimize svg further
Restore image-white icon and make sure images icons are SVG
Merge branch 'master' of github.com:guardian/frontend into remove-unused-icons

Conflicts:
	common/app/assets/stylesheets/theme/_icons.scss
Merge pull request #1101 from guardian/remove-unused-icons

Remove unused icons from sprite