Prevent easing example warnings.

Prevent easing example warnings.

examples/widgets/animation/easing was spitting out a lot of
"QEasingCurve: Invalid tcb curve" warnings.
The reason was that in case of the TCP curve we do not provide
defaults.

The function createEasingCurve() now provides reasonable values
for the custom curves to show what is possible and how to use them.

Change-Id: I880d8d0f0ce2872ce2019f7d2e000f4c4ce136e2
Reviewed-by: Mitch Curtis <mitch.curtis@digia.com>
Reviewed-by: Alessandro Portale <alessandro.portale@digia.com>