Timeline: show note for objects associated to period but without own dating
There could be many objects that belong to a period but which are currently not shown because they themselves are not dated otherwise. Maybe this can be shown as a 'footnote' to a bar on the timeline, something like (+ 13) if there are 13 more datings/objects of that period that do not have a concrete position on the timeline.
Related question: Should these objects/datings be counted for a period in the histogram?