Investigate changes after replacing `fancyhdr` with `scrlayer-scrpage`

[Wandmalfarbe]

With the changes introduced in #174, the book example now has header and footer (just text without rules) on all chapter pages. I don't know if this is a KOMA-Script default or not... I'll have to investigate.

Also in the example images-and-tables the numbers change from non serif to serif (look at the 10 % in the table or at the page number one). This might be introduced because the examples are rarely updated.