one-to-many graph: main book is shown at location 0 instead of date

[pverkind]

(assigning this to myself)

[pverkind]

make it an option to show the main book at location 0

[mabarber92]

Perhaps add a highlighted region in the graph for books by the author (self reuse), or a think line marking out the death date of the author (to avoid confusion with very dark dots elsewhere on the visualisation).