Revert "Merge pull request #4382 from guardian/revert-pull-request-4381"

This reverts commit d9227ca2dfa630e5cf6fe703c5488809595d2e38, reversing
changes made to 071544d6f5bf607f0195ddf277d726533e6be148.
URLencode SVG
Merge pull request #4519 from guardian/svg-sprite-optimisation-urlencoded

SVG sprite optimisation: urlencoded