Preparations for the new styling of the website

Related to #17 (closed)
Solves #66 (closed)

We have some general issues about styling the site that need to be addressed.

This is the first cosmetic surgery. We've removed unnecessary scss files and prepared the individual components for a component-based styling. There are a few small changes that affect many pages, such as adding ids to the main component of each page.

After this has been merged, I would suggest that we treat every single page in a separate merge request so that the changes stay small.