feat: re-add debug button/modal

Fixes #1687

js/src/common/components/RequestErrorModal.js

@@ -0,0 +1,30 @@
+import Modal from './Modal';
+
+export default class RequestErrorModal extends Modal {
+  className() {
+    return 'RequestErrorModal Modal--large';
+  }
+
+  title() {
+    return this.props.error.xhr
+      ? this.props.error.xhr.status+' '+this.props.error.xhr.statusText
+      : '';
+  }
+
+  content() {
+    let responseText;
+
+    try {
+      responseText = JSON.stringify(JSON.parse(this.props.error.responseText), null, 2);
+    } catch (e) {
+      responseText = this.props.error.responseText;
+    }
+
+    return <div className="Modal-body">
+      <pre>
+        {this.props.error.options.method} {this.props.error.options.url}<br/><br/>
+        {responseText}
+      </pre>
+    </div>;
+  }
+}