* IOT dashboard: Make light dimmer use arc renderer
* use shadow
* add value text
* add warm and cold parts
* add knob
* handle input
* only move knob when drawing along the arc
* improve input handling
* add tickmarks
* add tickmarks node
* clean up a bit
* Update screenshot of IOT dashboard for github site
* 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.
