Migrate from `Material-for-MKDocs` to `Zensical`

[FlorianK13]

It seems like the developers of Material-for-MKDocs are shifting their focus towards zensical. They say it is compatible with mkdocs setup. The problem is that the upwards dependency MKDocs is unmaintained.

Right now, zensical is in an early stage of development. But maybe we need to migrate to it at some point in time.

EDIT: Material-MKDocs is in maintenance mode now: squidfunk/mkdocs-material#8523

[FlorianK13]

Let's wait for a 0.x.0 release here at least.