Fix listen on AnyIP for url 0.0.0.0

[cocoon]

To listen on all available IPs this fix allows to use the following URL:

var settings = new WireMockServerSettings
{
    Urls = new string[] { "http://0.0.0.0:80" },
};
var server = WireMockServer.Start(settings);

I tried to add a test, but I think the test can be improved.
Could be split in a test for IPv4 and IPv6 and maybe the naming is not perfect.
Getting all IPs could be moved into a utility method ...
Feel free to improve afterwards.

[StefH]

Can you please resolve the comments which you did fix?

[StefH]

pls take a look at some extra comments

[StefH]

Thank you !