Make tree widget reusable without detail view

[lucas-koehler]

The tree widget should be properly usable without the rest of the editor (i.e. the detail view).

• Tree widget needs to be exported (likely already the case but needs to be verified)
• Tree widget needs to be configurable without the rest of the editor
• Tree widget needs to be configurable to not try to show something in the detail
• Potentially new utility method to create tree widget DI container without editor and detail.