pdate help documentation for Yioop 7.0

pdate help documentation for Yioop 7.0
Update README.txt, INSTALL.txt
Update composer.json for new PHP requirements
Lower MEMORY_FILL_FACTOR to reduce crashes
Tweak CSS for help to make work again under mobile.
Tweak Help.js to make case of no wiki page  for help item
work again.
Make proxy  crawling compatible with spam site detection.
Allow crawling of proxies with username password.
Notice suppression in PdfProcessor