Fixes#1486
* Adds the `Access-Control-Allow-Headers` response header to CORS responses for both **OPTIONS preflight requests** and any request containing an `Origin` header.
* The `Access-Control-Allow-Headers` response includes only the headers specified in the `Access-Control-Request-Headers` request header, always returned in lowercase.
* Fixes an issue with allow headers comparison in cors evaluation by making it case-insensitive.
* Adds missing unit tests for the **OPTIONS controller**.
3d20a63f75