Clean up models and provide abstractions

[cthoyt]

Summary

This PR does clean-up on many of the models I wasn't fast enough to get to before the PRs were merged

• [ ] Unit tests provided for these changes
• [ ] Documentation and docstrings added for these changes using the sphinx style

Changes

• Give a bullet point summary of the changes made in this PR

[benedekrozemberczki]

@cthoyt Tell me when you are ready and I will review and merge this PR.

[cthoyt]

@benedekrozemberczki I had a couple more things in mind but I suppose they can be done in a future PR. please take a look when you're ready