Add support for Memcached/Improve database cache

- Create Cache Driver interface
- Update cache table fields
- Add CacheSessionHandler

src/Core/Cache/ICacheDriver.php

@@ -0,0 +1,50 @@
+<?php
+
+namespace Friendica\Core\Cache;
+
+use Friendica\Core\Cache;
+
+/**
+ * Cache Driver Interface
+ *
+ * @author Hypolite Petovan <mrpetovan@gmail.com>
+ */
+interface ICacheDriver
+{
+	/**
+	 * Fetches cached data according to the key
+	 *
+	 * @param string $key The key to the cached data
+	 *
+	 * @return mixed Cached $value or "null" if not found
+	 */
+	public function get($key);
+
+	/**
+	 * Stores data in the cache identified by the key. The input $value can have multiple formats.
+	 *
+	 * @param string  $key      The cache key
+	 * @param mixed   $value    The value to store
+	 * @param integer $duration The cache lifespan, must be one of the Cache constants
+	 *
+	 * @return bool
+	 */
+	public function set($key, $value, $duration = Cache::MONTH);
+
+
+	/**
+	 * Delete a key from the cache
+	 *
+	 * @param string $key
+	 *
+	 * @return bool
+	 */
+	public function delete($key);
+
+	/**
+	 * Remove outdated data from the cache
+	 *
+	 * @return bool
+	 */
+	public function clear();
+}