code: @Nonnull
    public final UnifiedResponse setDownloadFilename (@Nonnull @Nonempty final String sFilename)
    {
      setMimeType (CMimeType.APPLICATION_FORCE_DOWNLOAD);
      setContentDispositionFilename (sFilename);
      return this;
    }
docs: Utility method for setting the MimeType application/force-download and set
  the respective content disposition filename.
  
  @param sFilename
  The filename to be used.
  @return this