Integrate Material for Mkdocs functionalities

[me-pic]

Closes #55
To preview those changes locally: mkdocs serve at the root (i.e., where the mkdocs.yml is)

Proposed Changes

• Set up Material of Mkdocs theme, which allow the possibility for collapsable sub-sections
• Add link to repo
• Add favicon
• Add dark mode

Change Type

• bugfix
• refactoring
• infrastructure
• documentation
• other

Checklist before review

• I added everything I wanted to add to this PR.
• [Documentation only] I built the docs locally.
• My contribution is harmonious with the rest of the code: I'm not introducing repetitions.
• My code respects the adopted style, especially linting conventions.
• The title of this PR is explanatory on its own, enough to be understood as part of a changelog.
• I added or indicated the right labels.

• I added information regarding the timeline of completion for this PR.

• Please, comment on my PR while it's a draft and give me feedback on the development!

[m-miedema]

This is working very well for me. I do think the navigation bar should be moved to the left as we discussed (helpful in making more dense sections more navigable and also reducing the unnecessary titles that are shown on the left when the navigation bar remains on top.)

The new physiopy logo icons are great!