add 403 and 404 routes to "Basic site settings"

guido_s → changed the visibility of the branch 1.0.0-beta1 to hidden.

guido_s → changed the visibility of the branch 1.0.0-beta1 to active.

guido_s → changed the visibility of the branch 3544410-add_403_and_404 to hidden.

The branch naming of this fork is not good here. There shouldn't be a branch named 1.0.0-beta1 for an issue. The other branch name (3544410-add_403_and_404) would be preferred. But the content of the branch is good and both install and uninstall hooks work fine and values for the error pages are set and removed as intended.
So I'm gonna merge this, but pay attention on future branch names please.