PDF encryption improvements

• Compilation of progressive PDF signatures, to improve PDF generation speed
• The PDF encryption option in the config.ini is disabled by default, to activate it, gpg needs to be installed and option PDF_STORAGE_ENCRYPTION must be set to true

@wincelau

Configuration verification page

This page is accessible via the url /administration , it is protected by IP authorization (localhost by default) in the ADMIN_AUTHORIZED_IP config.ini file.

It allows you to verify that all dependencies are properly installed.

@tale-fau

Full Changelog: v1.6.0...v1.6.1