[0.5.2] Setting node_name makes NomadNet crash on startup

[mehow]

0.5.2 introduced a bug where setting node_name in the config file makes NomadNet crash on startup with:
[Error] The configuration file is invalid. The contained exception was: invalid literal for int() with base 10: 'None'

In https://github.com/markqvist/NomadNet/blame/03a02a9ebc4fb1a2cc985bb48a7fb99b6d1bf5f5/nomadnet/NomadNetworkApp.py#L749 "node_name" needs to be replaced withoption.

[markqvist]

Thank you very much! Fixed!