The total time taken for a program should be the sum of durations of
events on the bottom of the stack. This is also what the flame graph
model does, and it results in useful percentages for total and self
times.

Recursion still has to be accounted for when showing the total time of
a specific event type, but we mark events with recursive calls and
show the time and percentage of recursion in the tooltip. As we already
showed binding loops on bindings and signal handlers before, this
integrates nicely.

Change-Id: Id4654e314bf86ce8bd06ceaaf93a67187c629adc
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>