Log Message:
Update tex-koma-script to 3.18

- Section command styles 'chapter' and 'part' allow to define new section
  commands with these styles or to redefine existing section commands using
  these styles

- New implementation of \chapter and \part defined using
  \DeclareSecionCommand. Caveat: This could break hacks that patch
  KOMA-Script's internal commands!

- New implementation of \addpart and \addchap

- several new layer attributes for scrlayer