* 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.
* IOT example, circular progress bar: Use a pen instead of a brush
That way we don't have to draw two circles, and we can in addition
use a conical gradient.
* IOT example: Make circular progress bar a QskControl
... and internally use a QskPaintedNode for now. By doing this we
already have the API ready (similar to QskProgressBar) and can
swap the QskPaintedNode with an arc renderer at a later point in
time.
