Add repr for objects like Simulator, Wells, Nodes and their derived classes.

**Is your feature request related to a problem? Please describe.**
The code below throws an error which whilst technically not a bug is not a great user experience as it is something I would expect a user to do.
```
from ResSimpy.Nexus.NexusSimulator import NexusSimulator
file_path = 'somemodel.fcs'
model = NexusSimulator(file_path)
print(model)
```

**Describe the solution you'd like**
Add an explicit repr onto objects like Simulator, Wells, Nodes and their derived classes.