added listen function for simple node

[JushBJJ]

There could also be times where the node is contacted from the outside world. Although I'm not sure if binding the socket to a public ip would be suitable for this repo, so I went for the local ip address.

Also added SimpleNode.connect command so its optional whether to either listen or connect to an address, however connecting will only require the host address because of self.port already configured in the SimpleNode __init__() arguments.