Update NWB Basics tutorial

[weiglszonja]

Extends the NWB File Basics tutorial with:

• merging the existing PR Update the index of the documentation  #1402 related changes with this branch
• more data types covered (e.g. Subject, SpatialSeries, Position)
• added UML diagrams to help understanding of inheritance, extensions
• merge existing tutorial sections with the beginning sections of nwb_tutorial
• removed the Units part (better to have it in the ecephys tutorial Update ecephys tutorial #1391)

Checklist

• Did you update CHANGELOG.md with your changes?
• Have you checked our Contributing document?
• Have you ensured the PR clearly describes the problem and the solution?
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• Have you checked to ensure that there aren't other open Pull Requests for the same change?
• Have you included the relevant issue number using "Fix #XXX" notation where XXX is the issue number? By including "Fix #XXX" you allow GitHub to close issue #XXX when the PR is merged.

[oruebel]

Just a heads up. I also made some changes to docs/gallery/general/file.py to merge the content of docs/source/overview_nwbfile.rst with the tutorial in the following PR #1402

[weiglszonja]

@oruebel Thanks for the heads-up! I'll close this PR and create a new tutorial page focusing on adding behavior data that is not covered yet in the tutorials (Subject, SpatialSeries, Position, etc.) or I can merge your changes here; What do you think?

[oruebel]

create a new tutorial page focusing on adding behavior data

@weiglszonja I agree, adding a tutorial focused on behavioral data will be useful. Depending on the scope that tutorial may fit well in the "Domain-specific tutorials" section.

BTW, if there are any changes from this PR that you think should remain part of the "NWB File basics" tutorial instead, then please feel free to make those changes in this or a new PR. I mainly wanted to give you a heads up about the other PR in case of merge conflicts. However, since the other PR mainly expands on the intro part of the "NWB File basics" tutorial, I don't think merging the changes should be too complicated.

[bendichter]

@rly can we enable this feature? https://docs.readthedocs.io/en/stable/pull-requests.html I don't have the readthedocs credentials (or don't know them)

[rly]

Please review: https://pynwb--1403.org.readthedocs.build/en/1403/tutorials/general/file.html#sphx-glr-tutorials-general-file-py

[bendichter]

@rly I made a few more adjustments. Good to go from my end!