MAINT: Rename examples and tutorials

[larsoner]

Adds automated redirect from plot_* to all of our examples, and renames them. @drammock for:

I should note that some, but not all, of the tutorials have had a number added to their filename, to enforce a specific sort order within their category. With the links changing anyway, now would be a good time to add numbers to the rest of them.

I implemented (but did not test) some custom_redirects code that you can use. I think you'll want to adapt it to take care of the number renaming. I added the conditional fname not in needed_plot_redirects.values() to the auto-plot_-redirect code, but you'll need to do a bit of testing to make sure things work. Can you take over and make the necessary code changes and git mvs?

closes #9082
closes #9290

[larsoner]

FYI @drammock I push-forced after a rebase

[drammock]

TODO:

• "modifying data in-place" is now in the intro category. It should be made much more general (right now it appears to be mostly a showcase for raw.apply_hilbert and raw.apply_function, neither of which appear in any other tutorials)
• the mne.Report tutorial is now in the intro category. It would benefit from a short introductory paragraph explaining what mne.Report is good for / why you might want to use it.
• 4DBTi phantom tutorial is missing its dipoles in the final figure (should open a separate issue/PR) part of Fix corrupted figures in plot_background_freesurfer_mne #9007
• Fix crossref to this sklearn tutorial which doesn't have a target name
• add all the redirects to the dict

[larsoner]

Fix crossref to this sklearn tutorial which doesn't have a target name

SG will give it one automatically:

$ python -m sphinx.ext.intersphinx https://scikit-learn.org/stable/objects.inv | grep ".*sphx_glr_auto.*blind_source_separation.*"
	sphx_glr_auto_examples_decomposition_plot_ica_blind_source_separation.py Blind source separation using FastICA   : auto_examples/decomposition/plot_ica_blind_source_separation.html#sphx-glr-auto-examples-decomposition-plot-ica-blind-source-separation-py

So you should be able to do something like:

:ref:`sphx_glr_auto_examples_decomposition_plot_ica_blind_source_separation.py`

[larsoner]

4DBTi phantom tutorial is missing its dipoles in the final figure (should open a separate issue/PR)

No need, I think this is a dup of #9007 . Will comment over there / in @GuillaumeFavelier's PR

[drammock]

@larsoner this appears to be working now in my local testing. Ready for review once CIs come back green.

[larsoner]

This has a conflict again unfortunately

[drammock]

@larsoner I've put in an upstream PR for the meta is undefined theme error: pydata/pydata-sphinx-theme#395

In the meantime I'll push a theme override here with the fix in place, to get Circle building again.

[larsoner]

@drammock there is another conflict but I'll fix + push + merge in quick succession once CircleCI comes back happy here

[larsoner]

Changed my mind, the build wasn't that far along

[drammock]

proof of concept: https://27567-1301584-gh.circle-artifacts.com/0/dev/auto_tutorials/misc/plot_ecog.html redirects to .../clinical/30_ecog.html

[larsoner]

Awesome work @drammock !

[agramfort]

🍾🍺🎉

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