4062: fix greedy infinite scrolling in tabs displaying more than one kind (Jobs and pipelines tab and Other objects tab).
Not only did scrolling never stopped, it never reloaded the next page and reloaded the same first page again and again.
Added test fixtures with many objects to test scrolling.
Added tests to use vertical scrollbar. The test itself is not able to test infinite scrolling by reloading the next page.
This may be because in integration testing new content is displayed only due to a click action.