Fix: Table could conitnually expand when x-scrolling was enabled. This was partly addressed in 6776, but the fix was incomplete as it would still occur on Safari Mac (possibly other browsers as well). This fix is very closely related to 8332 (hence commiting together as they are interdependent). Now use padding right on the header/footer wrapper to provide the overflow scroll ability, but only add it when a scrollbar is present - otherwise the width gets added on and we get the forever expanding table.
Dev: Unit tests - New tests for scrolling to ensure 6776 and 8332 don't occur again
