Allow commiting and then reusing a QTouchEventSequence for testing.

Allow commiting and then reusing a QTouchEventSequence for testing.

This method allows calls to stationary() to automatically remember
the previous position for a given touch point id. Example usage:

QTouchEventSequence sequence = QTest::touchEvent(&window);
sequence.press(0, QPoint(10,10)).commit();
sequence.stationary(0).press(1, QPoint(40,10)).commit();

Task-number: QTBUG-22057
Change-Id: I489ab3d61f4637d2ed97d09ed0854afa814407a1
Reviewed-by: Jason McDonald <jason.mcdonald@nokia.com>