Add gravity flow demo

backend/wordpress/wp-content/plugins/wp-mail-smtp/src/Admin/PageInterface.php

@@ -0,0 +1,45 @@
+<?php
+
+namespace WPMailSMTP\Admin;
+
+/**
+ * Class PageInterface defines what should be in each page class.
+ *
+ * @since 1.0.0
+ */
+interface PageInterface {
+
+	/**
+	 * URL to a tab.
+	 *
+	 * @since 1.0.0
+	 *
+	 * @return string
+	 */
+	public function get_link();
+
+	/**
+	 * Title of a tab.
+	 *
+	 * @since 1.0.0
+	 *
+	 * @return string
+	 */
+	public function get_title();
+
+	/**
+	 * Link label of a tab.
+	 *
+	 * @since 1.0.0
+	 *
+	 * @return string
+	 */
+	public function get_label();
+
+	/**
+	 * Tab content.
+	 *
+	 * @since 1.0.0
+	 */
+	public function display();
+}