* 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.
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