development/files_list_short: removed special case /home/user/Whonix/whonix_workstation/usr/local/bin/whonix_firewall,
because it has now a .d-style configuration folder.
development/files_list_short: expanded comment for /home/user/Whonix/whonix_shared/etc/fstab
whonix_gateway/usr/local/bin/whonix_firewall: moved configuration to /etc/whonix_firewall.d/. Adding sourcing of /etc/whonix_firewall.d/.;
new file, whonix_gateway/etc/whonix_firewall.d/10_default: added configuration (extracted from whonix_gateway/usr/local/bin/whonix_firewall)