Theme updates

The summary of changes during the 2022 course run

Before:

1. Search function was broken, which motivated an overhaul of the theme since I could not identify the bug initially.
2. Website template used a python script with jupyter notebook conversion, thebe executable cells, plotly javascript plots.
3. Long equations overflow horizontally

It turns out that plotly requirement to have require.js loaded to the header was breaking the mkdocs-material theme partially, and thus the search function, and thebe executable cells were not used at all. Importing a template with working plotly from Solid State Physics course required editing the math fences across the entire content, since it uses a different math plugin, so I adanbonded this approach, also because this mathforquantum content does not use plotly either.

I decided to use the generic mkdocs-material template and build the website bottom-up.

After:

1. Search works
2. No thebe, no python execute.py, no plotly support, now using "docs" folder for storing source file - no conversion required.
3. Updated Mathjax script and switched to SVG/CommonHTML mathjax rendering by default and included overflow-x: scroll. Equations are rendered much faster now and a clearer to read (CommonHTML), using the latest mathjax ver 2. script (2.7.7)
4. Added some theme minimal extensions for easier website navigation, toc flow (see mkdocs.yml)

Most of the work was done in the branch "enablingsearch" and merged during the course run, but after lecture notes were edited/updated.

Most of the work done on the content happened in the branch "maciejedits".

The snapshot of the website source with updated notes but before theme upgrade were backed-up into the branch "snapshot_preenablingsearch" for reference.