Directly save existing WebView content to PDF and A4 page size fix

This pull request adds the option to directly save the content of an existing WebView directly to PDF. By using this option there is no need to re-download or re-generate the content of an existing WebView when you are already displaying the content to the user. Also this fixed for me the problem that remote images in local generated HTML, where not saved to the PDF.

Secondly this pull request fixes extra blank pages when using A4 page size, by updating the page size to be more precise.

Regards Patrick