Several bug fixes and improved documentation

[zhu0619]

Changelogs

• Added the src_dataset_path attribute to the Curator for fully reproducible workflows.
• Fix serialization of the Curator.steps.
• Improved and added documentation in various places.
• Several other minor fixes.

---

Checklist:

• Was this PR discussed in an issue? It is recommended to first discuss a new feature into a GitHub issue before opening a PR.
• Add tests to cover the fixed bug(s) or the newly introduced feature(s) (if appropriate).
• Update the API documentation if a new function is added, or an existing one is deleted.
• Write concise and explanatory changelogs above.
• If possible, assign one of the following labels to the PR: feature, fix or test (or ask a maintainer to do it for you).

---

[cwognum]

Thanks @zhu0619! I left some comments. I have been quite nitpicky, but I think it's important to be very intentional and careful in the decisions we make early and the example we set. This will simplify our lives later on. I made an effort to explain all my considerations.