Rename private keys to protected

Otherwise the protected (private) metadatas will be published
fix pdf generation issue when wkhtmltopdf

This commit fixes an issue with the pdf generation when using wkhtmltopdf.
Prior to this commit wkhtmltopdf was using the wrong media type: `screen` instead of `print`.
In this commit we add the `--print-media-type` option to force wkhtmltopdf to use media print.
Merge branch 'tuxinaut-wkhtmltopdf_patched'