Update: rewrite firewall, adding support for custom chains

Update: rewrite firewall, adding support for custom chains

This is a major redesign of the firewall program.
Iptables chains are now supported automatically.
Each new basic list is itself a chain.
Reserved words not allowed for custom chains are:
- main
- stop
- lock

The 'main' chain signifies use of the default iptables chain.

The layout and structure of the files have been rewritten to utilize chains.
The default-firewall file has been removed and replaced with the following files:
- firewall-first
- firewall-last
- firewall-other

The newly written rules defines default firewall rules and chains such that there the following self-explanatory chains:
- input-tcp
- input-udp
- input-icmp
- output-tcp
- output-udp
- output-firewall

In addition to the above changes, the base functionality has been broken up into smaller functions to improve code quality.