Currently the `getnetworkinfo` returns something like: 

```
"localservices": "0000000000000449",
```

Manually parsing this consistently gives me a headache (see also https://github.com/sipa/bitcoin-seeder/pull/77).

It would be useful to parse this and show the right combination of `NODE_NETWORK`, `NODE_GETUTXO`, `NODE_BLOOM`, `NODE_WITNESS`, `NODE_NETWORK_LIMITED` and `NODE_COMPACT_FILTERS`. In addition the help text for `getnetworkinfo` could be expanded to mention the right BIP numbers for known flags.

There is some ad hoc parsing to populate e.g. `localrelay`, etc (?).  Their help text could also refer back to `NODE_GETUTXO`.

See also: https://en.bitcoin.it/wiki/Protocol_documentation#Network_address
const std::string& name,
        const Type& type,
        const Fallback& fallback,
        const std::string& description,
        const std::string& oneline_description = "",
        const std::vector<std::string>& type_str = {})
        : m_name{name},
          m_type{type},
          m_fallback{fallback},
          m_description{description},
          m_oneline_description{oneline_description},
          m_type_str{type_str}
    {
        assert(type != Type::ARR && type != Type::OBJ);
    }
    RPCArg(