Check for duplicate slugs in case-insensitive way.
Check for duplicate slugs in case-insensitive way.

Part of the way to fixing #40

Impactstory/total-impact-webapp,total-impact/total-impact-webapp,total-impact/total-impact-webapp,Impactstory/total-impact-webapp,total-impact/total-impact-webapp,Impactstory/total-impact-webapp,total-impact/total-impact-webapp,Impactstory/total-impact-webapp