[WIP][DOC] add structure to example gallery

[dengemann]

As discussed earlier, this adds sections to the gallery. Some fine-tuning may be needed. Let's see if build works here. cc @bruAristimunha @robintibor

[codecov]

Codecov Report

Merging #470 (f743484) into master (550ce1b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #470   +/-   ##
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  Coverage   84.41%   84.41%           
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  Files          60       60           
  Lines        4357     4357           
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  Hits         3678     3678           
  Misses        679      679           

[bruAristimunha]

closes #455

[bruAristimunha]

Hi @dengemann!

Can I work in the PR?

[dengemann]

Sure go ahead!

[bruAristimunha]

Hi @dengemann, @robintibor, @martinwimpff and @agramfort,

I think I finished the re-organization of the documentation. During the process, I re-created the installation pages. Fixed something related to skorch and the examples. I fixed something that was disabled or not working in the documentation, e.g., institutions on the front page and the source button. And several small details. Can you please check? I think it would be nice to have the new documentation integrated ASAP to focus on the other tasks for the code sprint. 🙏🏽

I thank you in advance for your time reviewing.

[bruAristimunha]

Here is the link for the artifact: https://github.com/braindecode/braindecode/suites/15663207492/artifacts/894131735 . @dengemann, @agramfort and @martinwimpff