Freefall gesture needs to be initialized into plugin to be usable

This fixes the flaky unit test failures. It also adds freefall to
unit test.

Task-number: QTBUG-32108
Change-Id: Ia1ee852b1e57b937fd7368073e259a139da9a697
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>
Reviewed-by: Thomas McGuire <thomas.mcguire@kdab.com>