Reduce the maximum time to flick to 200 ms

Merged Alex Rosca requested to merge roscale/okular:flick_max_time into release/20.12

When making a flick using the mouse or the touchscreen and then slowly dragging the pages in the same direction with the flick, it unintentionally reenters the flicking state after a mouse button release and it's quite annoying. The commit reduces the maximum time before the next flick.

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