Add a first empty state to the discussion list

js/lib/components/Placeholder.js

@@ -0,0 +1,19 @@
+import Component from 'flarum/Component';
+
+/**
+ * The `Placeholder` component displays a muted text with some call to action,
+ * usually used as an empty state.
+ *
+ * ### Props
+ *
+ * - `text`
+ */
+export default class Placeholder extends Component {
+  view() {
+    return (
+      <div className="Placeholder">
+        <p>{this.props.text}</p>
+      </div>
+    );
+  }
+}