* add QskArcNode and QskArcRenderer
* IOT example: Use QskArcNode instead of own arc node
* move some functionality to the arc renderer
* add QskArcMetrics
* add methods to QskSkinlet
* remove circular bar graph node
We can now use updateArcNode() and don't need our own method.
* support linear gradients in the arc renderer
* clean up
* incorporate Uwe's changes
* add overloads for updateArcNode() when the angles are set dynamically
The angles don't always come from the style, so we need overloads
in QskSkinlet to set them dynamically.
Uwe Rathmann
Peter Hartmann