Timeline: correctly find the timeRange
Correctly find the earliest and latest years that need to be displayed on the timeline.
At the moment we sort in ascending order of the start dates of all timespans. Then we determine the timeRange based on the first value of the first object and the second value of the last object in the sorted data. But there are cases where objects start earlier but last longer than the latest-starting object, ergo the end of timeRange is currently incorrect.