Add IStorage interface

storage classes should implement this interface

src/Model/Storage/IStorage.php

@@ -0,0 +1,35 @@
+<?php
+/**
+ * @file src/Model/Storage/IStorage.php
+ * @brief Storage backend system
+ */
+
+namespace Friendica\Model\Storage;
+
+/**
+ * @brief Interface for storage backends
+ */
+interface IStorage
+{
+	/**
+	 * @brief Get data from backend
+	 * @param string  $ref  Data reference
+	 * @return string
+     */
+	public static function get($ref);
+
+	/**
+	 * @brief Put data in backend as $ref. If $ref is null a new reference is created.
+	 * @param string  $data  Data to save
+	 * @param string  $ref   Data referece. Optional.
+	 * @return string Saved data referece
+	 */
+	public static function put($data, $ref = null);
+
+	/**
+	 * @brief Remove data from backend
+	 * @param string  $ref  Data referece
+	 * @return boolean  True on success
+	 */
+	public static function delete($ref);
+}