Tooltips shown while selecting should show information about the selection

[fqueze]

The tooltip on the Power tracks only show one line with the instantaneous power in watt. While selecting a range, it would be nice if the tooltip could also show the energy used during that selected range, in watthour. Showing the average power over the selected range (or the current range when the user is not selecting) could also be interesting.

I think this could also apply to other charts, for example the tooltip of the memory chart could show the "memory range" over the range being selected rather than over the entire current range.

The point of adding this information in the tooltip is to allow easy measurements by just selecting a range and reading the value in the tooltip.