## Summary
- Add public API for adding, removing, connecting and disconnecting nodes in the network.
- Introduce parent of simcomponent to keep track of parent as per this diagram 
- Update tutorial notebook with new way of doing things.
## Test process
Unit and integration tests written and passing.
## Checklist
- [x] This PR is linked to a **work item**
- [x] I have performed **self-review** of the code
- [x] I have written **tests** for any new functionality added with this PR
- [x] I have updated the **documentation** if this PR changes or adds functionality
- [ ] I have written/updated **design docs** if this PR implements new functionality
- [ ] I have update the **change log**
- [x] I have run **pre-commit** checks for code style
Related work items: #1798
- Added .show() methods to new router classes to enable inspection of the components as you would a real router.
- Removed gateway from the NIC and added default_gateway to Node so that Node has a single default gateway.
- Added some routing tests to check that ping can be performed when router between subnets.
## Summary
- Add an object that holds the entire simulation, and a container for the network that keeps track of a list of nodes and links.
- Implement `describe_state()` for all existing sim components and take advantage of the inheritance relationships to avoid repetition.
- Fix some minor mistakes like typehints and indentation errors.
- Write a jupyter notebook which uses the python API to create a simulation and verify that it's `describe_state()` method outputs a correct value.
- Currently the notebook creates the simulation in a janky way, because the API for simulation creation is not fleshed out yet. Further tickets have been added to the backlog to address some of these shortcomings. They are:
- #1790
## Test process
I have tested that the notebook runs and that after populating a simulation, the describe_state function returns a dictionary full of only serialisable data types.
## Checklist
- [y] This PR is linked to a **work item**
- [y] I have performed **self-review** of the code
- [~] I have written **tests** for any new functionality added with this PR
- [n] I have updated the **documentation** if this PR changes or adds functionality
- [na] I have written/updated **design docs** if this PR implements new functionality
- [y] I have update the **change log**
- [y] I have run **pre-commit** checks for code style
Note:
This ticket also makes a small amount of progress against: #1705, it adds a shell of a network class, but only by creating the class, not implementing any functionality.
Related work items: #1787
