Make sure to display relevant content, even if it is not present in the navigation

If a certain portal type is globally excluded from the navigation (e.g. via @@navigation-controlpanel), we need to make sure that items of this type still get displayed in the folder-tree if there is an explicit filter for them.

*Simple use case for explanation*: A Choice field with `source=ObjPathSourceBinder(portal_type='Image')`, and Images being excluded from the navigation.

Since the query for the folder tree is built using INavigationQueryBuilder, images are not displayed, even though we explicitly want to filter for them.

This pull request should fix that.