Changes to node_settings.py

- [x] [Nodes now maintain a minimum and maximum version too](https://github.com/BrendanParmer/NodeToPython-Dev-Tools/issues/7)
- [x] [Move `ST` enum to `node_settings.py`](https://github.com/BrendanParmer/NodeToPython-Dev-Tools/issues/9)
- [x] [Move `NTPNodeSetting` class definition to `node_settings.py`](https://github.com/BrendanParmer/NodeToPython-Dev-Tools/issues/10)