Add ghostscript pre-printing to the pdfconverter container

We have several problems where pdf2HtmlEX is not working properly anymore, e.g. because PDFs are of a new standard with newer features (e.g. mixed Colormodes) or it crashes when detecting fonts. All of these could be fixed when printing the pdf to file with ghostscript before converting it, so we should add that as an option to the pdfcontainer. The pdf should be pre-printed with ghostscript in the container either when the pdf2htmlEx conversion fails to reattempt the conversion or simply every time a conversion is done. This behaviour should be configurable via a config-option in T5 "runtimeOptions.plugins.VisualReview.pdfPrePrintAlways" [0|1]

https://stackoverflow.com/questions/40376772/using-php-how-i-check-a-pdf-file-contents-is-valid-or-invalid
https://stackoverflow.com/questions/28478975/how-to-get-pdf-version-with-ghostscript-gs-on-linux