Restructure/simplify plot_file gallery

[rly]

Motivation

The NWB basics tutorial is good but had a little too much detail. More detail than we typically explain in the ~20 minute introduction in our events.

• removed timestamps linking. that is covered in https://pynwb.readthedocs.io/en/stable/tutorials/advanced_io/linking_data.html#sphx-glr-tutorials-advanced-io-linking-data-py, though we could create a more user-friendly how-to doc that has just this snippet in it
• removed epochs and time intervals (kept trials). these are covered in https://pynwb.readthedocs.io/en/stable/tutorials/general/plot_timeintervals.html#sphx-glr-tutorials-general-plot-timeintervals-py and were mostly copied from there
• removed references to NWBDataInterface, NWBContainer, and NWBData. These are low-level abstractions and not really user-facing. Because they are not user-facing, they are not counted in our U24 milestones so they are safe to remove.
• moved the I/O to the end rather than the middle. it flows better and better matches the matnwb intro tutorial

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?
• Is your contribution compliant with our coding style? This can be checked running flake8 from the source directory.
• 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.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.88%. Comparing base (04a6506) to head (130678c).
Report is 21 commits behind head on dev.

Additional details and impacted files

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  Coverage   91.88%   91.88%           
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  Files          27       27           
  Lines        2651     2651           
  Branches      692      692           
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  Hits         2436     2436           
  Misses        142      142           
  Partials       73       73           

Flag	Coverage Δ
integration	72.80% <ø> (ø)
unit	83.96% <ø> (ø)

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[rly]

Workflow notes:

• Check Sphinx Links workflow is failing because of a new warning in the CI. For the sake of merging this for the presentation tomorrow, I will merge this now and address the warning in a separate PR.
• The Conda issues appear to be due to a random and unrelated unsafe threading issue.