Add flick(xVelocity, yVelocity) and cancelFlick() functions.
The functionality provided by these functions is already covered
by current unit tests.

Task-number: https://bugreports.qt.nokia.com/browse/QTBUG-23865


Change-Id: Ie284232bfbd98ae7c70ca060760fb016b4a45ee1
Reviewed-by: Martin Jones <martin.jones@nokia.com>