Documentation improvements and fixes

[rafmudaf]

General documentation improvements and fixes

This pull requests is a set of changes to the documentation to address some issues and improve particular areas. The included changes are:

• Increase the number of colors used in the plots in https://rafmudaf.github.io/floris/wake_models.html. In the current docs, the contour levels are very discrete.
• The "floris_101" notebook is renamed to "intro_concepts"
• Following the change above, an "advanced_concepts" notebook is added
• Fix out of date architecture diagrams
• Add guidance for adding a new wake model based on Wake model #547
• Drop the custom templates introduced in Move docs to Jupyter Book and expand content #514 and referenced in the bug report in Jupyter Book version bug with custom templates #635
• Remove unused documentation dependencies and let the theme version numbers float to always get new updates

A live version of the site is available at https://rafmudaf.github.io/floris/.

Related issue

Addresses #635

Impacted areas of the software

Documentation site

[misi9170]

Thanks Raf!