allow to set class of knob div

Author: milahu

src/Knob.svelte

@@ -1,4 +1,4 @@
-<div class="knob-control" style="{style}" bind:this={knob}>
+<div class:knob-control={true} class={_class} style={style} bind:this={knob}>
     <svg width="{computedSize}" height="{computedSize}" viewBox="0 0 100 100"
         on:click="{onClick}"
         on:mousedown="{onMouseDown}"
@@ -74,6 +74,8 @@ export let textColor = '#000000';
 export let strokeWidth = 17;
 export let valueDisplayFunction = (v) => v;
 
+$: _class = $$restProps['class'];
+
 onMount(async () => {
     dashLength()
     clearInterval(interval);