Rewrite the configuration file and the make file

[lionelkusch]

My notes on this file:

• check if you still need numpydoc
• remove commented lines (72, 162-173, 264-267)
• define a them for the documentation
• change the link in the navbar
• remove the latex option
• remove the dependence to pyvista and mne
• check if the configuration gallery option is correct

[lionelkusch]

For the Makefile:

• check the value of variables at the beginning

[bthirion]

I'm not a guru in config files, so I'm happy to hear from more knwoledgeable people.

[lionelkusch]

As example: https://learn.scientific-python.org/development/guides/docs/

[lionelkusch]

numpydoc can be replaced by sphinx.ext.napoleon

[lionelkusch]

For the selection of a theme for the documentation: https://sphinx-themes.org/