Doctype section has no default selection

CMS-9311 involved the synchronization of section, listing, tabs and selected "document". When demo'ing the fix, we noticed that while the section and listing seem to be in sync most of the time, switching to the doc type section (initially) doesn't update the listing. Only when a node in the doc type tree is selected, the listing gets updated. The section remembers the selection, which will affect the listing upon retuning to the doc type section.

For UI consistency, the doc type section should have a default selection, affecting the listing component.