Templates: implement green+red behavior even with only one interface. Refs #2861
createlinks: execute firewall-adjust on network-* events. Regs #2861
spec: provides nethserver-firewall. Refs #2873
Firewall lib: disable providers associated to non-existing red interface. Refs #2852
Web UI: disable providers associated to non-existing red interface. Refs #2852
Web UI: avoid reuse of already associated red interfaces. Refs #2852
Merged into master. Refs #2873 #2861
Merged into master. Refs #2852