Opal vulnerable to CSRF protection bypass

Opal is OBiBa’s core database application for biobanks or epidemiological studies. Prior to version 5.1.1, the protections against cross-site request forgery (CSRF) were insufficient application-wide. The referrer header is checked, and if it is invalid, the server returns 403. However, the referrer header can be dropped from CSRF requests using `<meta name="referrer" content="never">`, effectively bypassing this protection. Version 5.1.1 contains a patch for the issue.