Update error message when the nodes are not loaded
<template>
<div>
<Tree class="wptree" :data="treeData" :config="treeConfig" :key="Math.random()">
- <Placeholder>Your processing tree has no nodes.</Placeholder>
+ <Placeholder>Could not open your Tornado configuration.</Placeholder>
</Tree>
<!-- <DisplayAsJson :obj="treeData"/> -->
</div>
