Merged in feature/from-pantheon (pull request #16)

code from pantheon

* code from pantheon

wp/wp-content/plugins/wordpress-seo/src/promotions/application/promotion-manager-interface.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace Yoast\WP\SEO\Promotions\Application;
+
+/**
+ * Interface for the promotion manager.
+ */
+interface Promotion_Manager_Interface {
+
+	/**
+	 * Whether the promotion is effective.
+	 *
+	 * @param string $promotion_name The name of the promotion.
+	 *
+	 * @return bool Whether the promotion is effective.
+	 */
+	public function is( string $promotion_name ) : bool;
+
+	/**
+	 * Get the list of promotions.
+	 *
+	 * @return array The list of promotions.
+	 */
+	public function get_promotions_list() : array;
+}