Fix typo in Context2D documentation.

Change-Id: Ib6e2436ba383a2caf78ac359883338016c2b7668
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Added a signal handler

Without the onHeightChanged signal handler the transition
of the NumberPad from left to right is incomplete especially
on a mobile device where the window is scaled to fit the view.
So the NumberPad ends up hidden behind the Display.

Task-number: QTBUG-36086
Change-Id: Iab021c9f2572a4ac83bc393dddc24ddd31849cb4
Reviewed-by: Niels Weber <niels.weber@digia.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>