PDF processor now generates HTML

The old image-based PDF processor has been replaced with one
that uses `pdf2htmlEX` and generates an html file for each page.
Cleaned up config.js jsdoc and PDF processor
Fixed-up the jsdoc for timeouts in ./config.js.
Expanded the filters than can be applied when reprocessing content
Merged master in pdf2html
Add more JSDoc for the new filtered reprocess previews endpoint
Added more test coverage for the regenerate previews filters
Merged master into pdf2html
Merge pull request #654 from simong/pdf2html

PDF processor now generates HTML