Vue Comments: Comments ported to Vue + DnD fileupload

* Drag and drop files to comment editor to add a file attachment
* Using Vue to render comments

Since comments now has attachments we need to update the schemas
./manage.py maintenance replace_pillar_node_type_schemas

src/scripts/js/es6/common/vuecomponents/utils/GenericPlaceHolder.js

@@ -0,0 +1,13 @@
+const TEMPLATE =
+`<div class="generic-placeholder" :title="label">
+    <i class="pi-spin spin"/>
+    {{ label }}
+</div>
+`;
+
+Vue.component('generic-placeholder', {
+    template: TEMPLATE,
+    props: {
+        label: String,
+    },
+});