Added CORS support
The process engine did not send CORS (Cross-origin resource sharing) header fields in the response header.
Front-end uses iframes, which requires CORS support for sharing resources between iframes. Until now, CORS support was provided by the reverse proxy (see cors.conf), which is unused for a personal installation of the DECODER Project tool-chain using docker-deployment.
This commit adds support for CORS, and address Issue #4 (closed).