Make the code robust against duplicated timeouts

[PetrDlouhy]

There is number of cases (i.e. two buttons triggering same dropdown) when the code would set up multiple timeouts at the same time. This can easily lead to weird and unexpected behavior such as dropdown hiding at unexpected moments when the mouse is still hovering over the active elements.

If we keep all the timeouts in array and clear all of them all of them, it would make the code robust against such problems. I expect that even the stop this event if conditions might not be needed anymore.