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
}
        case Type::AMOUNT: {
            ret += "numeric or string";
            break;
        }
        case Type::RANGE: {
            ret += "numeric or array";
            break;
        }
        case Type::BOOL: {
            ret += "boolean";
            break;
        }
        case Type::OBJ:
        case Type::OBJ_USER_KEYS: {
            ret += "json object";
            break;
        }
        case Type::ARR: {
            ret += "json array";
            break;
        }
            
        }
    }
    if (m_fallback.which() == 1) {
        ret += ", optional, default=" + boost::get<std::string>(m_fallback);
    } else {
        switch (boost::get<RPCArg::Optional>(m_fallback)) {
        case RPCArg::Optional::OMITTED: {