Regression: Hst configuration editor cannot pick documents any more for sitemap items

HstContentPickerDialog tests whether the document to pick is of type SoftDocument and whether it contains a ancestor node with name hst:site. If the above assertion fails, the 'ok' button is not highlighted

Since HST access content over canonical layers, the above assertion are not correct any more, making the hst config editor unable to select a document.

Also in the tree hippo:translation nodes are shown