feat: merge store with props

* if options are passed to useVueFlow, we want to merge them with possibly passed props
* renamed flowStore to stateStore
* fix examples
* add store prop to pass an already existing store to flow

Signed-off-by: Braks <78412429+bcakmakoglu@users.noreply.github.com>

examples/RGBFlow/RGBOutputNode.vue

@@ -10,7 +10,7 @@ const props = defineProps<RBGOutputNodeProps>()
 <template>
   <div :style="{ backgroundColor: props.rgb }" class="rgb-output-node">
     <div class="text-md uppercase">{{ props.rgb }}</div>
-    <Handle type="source" :position="Position.Left" />
+    <Handle type="target" :position="Position.Left" />
   </div>
 </template>
 <style>