Switch ExtractorPDF and ExtractorPDFContent to pdfbox

[ato]

ExtractorPDF is using a very old version of itext from 2006. Updating it to the newer version of itext used in contrib would require distribution of core Heritrix to come under the AGPL.

Apache PDFBox is Apache 2 licensed, is actively maintained and used by other widely adopted tools like Apache Tika. So this PR changes both PDF extractors to use the latest version of PDFBox instead.

Neither extractor is enabled by the default configuration so this likely doesn't affect many users.