Add Content-Security-Policy for sandboxed iframes to prevent info leaks
Add Content-Security-Policy for sandboxed iframes to prevent info leaks

jonboiser/kolibri,mrpau/kolibri,indirectlylit/kolibri,learningequality/kolibri,benjaoming/kolibri,mrpau/kolibri,mrpau/kolibri,benjaoming/kolibri,DXCanas/kolibri,lyw07/kolibri,jonboiser/kolibri,indirectlylit/kolibri,lyw07/kolibri,DXCanas/kolibri,lyw07/kolibri,jonboiser/kolibri,learningequality/kolibri,indirectlylit/kolibri,benjaoming/kolibri,lyw07/kolibri,learningequality/kolibri,jonboiser/kolibri,benjaoming/kolibri,DXCanas/kolibri,mrpau/kolibri,indirectlylit/kolibri,learningequality/kolibri,DXCanas/kolibri