Added access control headers in dev mode

no refs

- adds `access-control-allow-origin: *` headers for dev mode
- portal script will be loaded with `cross-origin=anonymous`, access control header is needed to allow script to load
- mimics unpkg which already adds `access-control-allow-origin: *`

ghost/portal/scripts/dev-mode.js

@@ -200,6 +200,9 @@ function startDevServer() {
                     headers: [{
                         key: 'Cache-Control',
                         value: 'no-cache'
+                    },{
+                        key: 'Access-Control-Allow-Origin',
+                        value: '*'
                     }]
                 }
             ]