admin breadcrumbs

[dbu]

for the menu admins, we have a breadcrumb functionality that shows the tree of the breadcrumbs in the navigation. this would make sense for other types of documents too. as phpcr is always a tree, we could always show parents. maybe as an admin extension or trait?

an open question is where to stop, if we should allow configuring a list of classes/interfaces that we want in the breadcrumb and stop when we encounter something else. and/or a maximum number of parents to show.