feat(prejoin_page) Add settings buttons

This reverts commit faf24ca7ec.

react/features/settings/components/web/audio/TestButton.js

@@ -0,0 +1,26 @@
+// @flow
+
+import React from 'react';
+
+type Props = {
+
+    /**
+     * Click handler for the button.
+     */
+    onClick: Function,
+};
+
+/**
+ * React {@code Component} representing an button used for testing output sound.
+ *
+ * @returns { ReactElement}
+ */
+export default function TestButton({ onClick }: Props) {
+    return (
+        <div
+            className = 'audio-preview-test-button'
+            onClick = { onClick }>
+            Test
+        </div>
+    );
+}