webview: small typo in log message
loader: do not start/stop network service discovery each time

The service seems pretty unstable. Let's keep run it in the
background. We have to track ourselves when a service becomes
unavailable and this is quite difficult since we don't have a lot of
information to know if the service that is gone is the service we are
using...
loader: build ping URL in a sensible way

Use `java.net.URL` to build the URL. We are now IPv6 compliant. We also
remove a bug with use use of `InetAddress.toString()` that was incorrect
since it tries to append the hostname if available. We always use the
host address.