limit Onionoo default listening to localhost

This means shipping a jetty.xml with the following change:

      <New class="org.eclipse.jetty.server.ServerConnector">
        <Arg>
          <Ref id="server"/>
        </Arg>
        <Set name="port">8080</Set>
+       <Set name="host">127.0.0.1</Set>
      </New>