Add description field for ports

In the settings, we config ports like:

```
[port:1]
port.enabled = False
port.type = serial
port.framing = kiss
kiss.checksum = false
serial.device = /tmp/vmodem_A0
serial.speed = 9600
```

We should add a text description as well, e.g. "144.43 link to Joe N0CALL". This should be added to PortConfig in settings.py