Fix #1595: allow blob: URLs in CSP to download zip files from editor iframe
Fix #1595: allow blob: URLs in CSP to download zip files from editor iframe

mozilla/thimble.mozilla.org,mozilla/thimble.mozilla.org,humphd/thimble.mozilla.org,humphd/thimble.mozilla.org,humphd/thimble.mozilla.org,mozilla/thimble.mozilla.org,mozilla/thimble.mozilla.org,humphd/thimble.mozilla.org