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/api/markdown.js

@@ -0,0 +1,17 @@
+function thenMarkdownToHtml(markdown, attachments={}) {
+    let data = JSON.stringify({
+        content: markdown,
+        attachments: attachments
+    });
+    return $.ajax({
+        url: "/nodes/preview-markdown",
+        type: 'POST',
+        headers: {"X-CSRFToken": csrf_token},
+        headers: {},
+        data: data,
+        dataType: 'json',
+        contentType: 'application/json; charset=UTF-8'
+    })
+}
+
+export { thenMarkdownToHtml }