Feature: Add port status to Node marker attribute

[MeijeSibbel]

Although sometimes the bridge can see the node, the UPnP/TCP or tunnel port is not always open, meaning that the node will not be able to connect to the network. Adding a port number to the marker attribute, making the text color green and adding a string that says "open" when the port is open and red when it is closed would directly allow a farmer to troubleshoot his node. This would require a port checker API that combines the node address with the port.