Permissions to create and display PDF file

Added adjustable permissions check in front of displaypdf user controller function. (Defaults to not to check).

One possible usage - if set ACCESS_COMMENT required permissions, then only registered users can download pdf files.
Also prevent search engines to index pdf files. They like to index pdf files, but possibly we don't, because they have same content, and because creating them consumes really very much processor time, and downloading them - bandwidth.