squid / WPAD: Add exception-files for generation of proxy.pac

squid / WPAD: Add exception-files for generation of proxy.pac

This patch extends the script /srv/web/ipfire/cgi-bin/proxy.cgi by additional code for reading exceptions for URL's and IP's/Subnets from two new files:

- /var/ipfire/proxy/advanced/acls/dst_noproxy_url.acl
- /var/ipfire/proxy/advanced/acls/dst_noproxy_ip.acl

as described in: https://wiki.ipfire.org/configuration/network/proxy/extend/add_distri

These can be used to define additional URL's, IP's and Subnets that should be retrieved "DIRECT" and not via the proxy. The files have to be created by the user, as the WPAD-Feature is not enabled by default anyway. If the files are not present or their size is 0, nothing is done. I'll revise the wiki-page, after the patch is merged and the core update is released.

Signed-off-by: Alexander Koch <ipfire@starkstromkonsument.de>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>