Add 'false' as a valid option in 'dport_limit'

I'm not sure why I cannot pass "False" bool value using a variable via
role dependency, but this will add a workaround for that in a ferm
template that requires this functionality.
Enable new dependency configuration in 'sshd' role

Now 'sshd' role will use new configuration options added in 'ferm' and
'tcpwrappers' roles. You can use 'sshd_*_allow' variables to define
lists of hosts that will have unlimited access to SSH service.
Make custom filenames in ferm templates consistent
Merge pull request #30 from drybjed/role/sshd

Updates in 'sshd' and 'ferm' roles
Add 'ferm' dependency in 'nginx' role

nginx role will use ferm role to configure access to HTTP/HTTPS in
iptables firewall.
Merge pull request #31 from drybjed/role/nginx

Add 'ferm' dependency in 'nginx' role