advanced importer support for FortiGate API

[tpurschke]

• [x] cactus fortigate fortios 5.6 is too old for testing (must be >=6.2, according to https://docs.fortinet.com/document/fortigate/7.0.2/fortios-release-notes/760203/introduction-and-supported-models, 7.0.2 supports our FWF-60E, but according to https://docs.fortinet.com/upgrade-tool we need 8 upgrade steps)
• [x] provide importer with basic functionality
• [x] make policy package name fixed in UI: we assume a single policy per FortiGate
• [x] document in help pages
• [x] v4 group support
• [x] v6 group support
• [x] service group support

Advanced

• [x] ipv6 support
• [ ] deal with protocol "ALL": fOS_servic:normalize_: 87] Unknown service found: webproxy, proto: ALL {'name': 'webproxy', 'q_origin_key': 'webproxy', 'proxy': 'enable', 'category': 'Web Proxy', 'protocol': 'ALL', 'helper': 'auto', 'iprange': '0.0.0.0', 'fqdn': '', 'tcp-portrange': '0-65535:0-65535', 'tcp-halfclose-timer': 0, 'tcp-halfopen-timer': 0, 'tcp-timewait-timer': 0, 'tcp-rst-timer': 0, 'udp-idle-timer': 0, ...}
• [ ] deal with rules with multiple zones (currently only the first zone is used)
• [ ] handle threat feeds if possible: FWORCHAlert - "source": "import", "title": "object reference error", "description": "found a broken object reference 'threat-feed1'
• [ ] get NAT information
• [ ] get gw interface & routing