Updated translations for SumatraPDF french webpages

I updated  :news-fr.html, sumpdf-latest.txt, and fixed a few typos in downloadafter-fr, download-free-pdfviewer-fr, free-pdfreader-fr and manual-fr. 
I also translated settings.html and settings2.3.html (and modified consequently links to those files into links to the french version  where necessary).

It's the first time I do that sort of job, so please be indulgent … 

Best regards,
B. Alfonsi