NetworkError should be more specific

[Anton-4]

There can be useful data behind a NetworkError, for example:

hyper::Error(
        Connect,
        ConnectError(
            "dns error",
            Custom {
                kind: Uncategorized,
                error: "failed to lookup address information: Name does not resolve",
            },
        ),
    ),

We should not discard that kind of data.

To start of simple, we can change NetworkError to NetworkError Str.