[IMP] website_slide, website : move the PDFJS library from slides to the...

[IMP] website_slide, website : move the PDFJS library from slides to the website module to allow reusing it in website modules.

This huge library handle PDF file to display them, count their pages, ... Due to its size, the lib is declared in a separated optional bundle who should be called with a 't-call-assets' only on the page it is required.