Add Session Management instances (including Depenency Injection)

- Prerequesite for mocking Sessions
- Reduce "App" class complexity

src/Core/Session/ISession.php

@@ -0,0 +1,70 @@
+<?php
+
+namespace Friendica\Core\Session;
+
+use Friendica\BaseObject;
+
+interface ISession
+{
+	/**
+	 * Start the current session
+	 *
+	 * @return self The own Session instance
+	 */
+	public function start();
+
+	/**
+	 * Checks if the key exists in this session
+	 *
+	 * @param string $name
+	 *
+	 * @return boolean True, if it exists
+	 */
+	public function exists(string $name);
+
+	/**
+	 * Retrieves a key from the session super global or the defaults if the key is missing or the value is falsy.
+	 *
+	 * Handle the case where session_start() hasn't been called and the super global isn't available.
+	 *
+	 * @param string $name
+	 * @param mixed $defaults
+	 * @return mixed
+	 */
+	public function get(string $name, $defaults = null);
+
+	/**
+	 * Sets a single session variable.
+	 * Overrides value of existing key.
+	 *
+	 * @param string $name
+	 * @param mixed $value
+	 */
+	public function set(string $name, $value);
+
+	/**
+	 * Sets multiple session variables.
+	 * Overrides values for existing keys.
+	 *
+	 * @param array $values
+	 */
+	public function setMultiple(array $values);
+
+	/**
+	 * Removes a session variable.
+	 * Ignores missing keys.
+	 *
+	 * @param string $name
+	 */
+	public function remove(string $name);
+
+	/**
+	 * Clears the current session array
+	 */
+	public function clear();
+
+	/**
+	 * Kills the "Friendica" cookie and all session data
+	 */
+	public function delete();
+}