Add support for Memcached/Improve database cache

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

src/Core/Cache/DatabaseCacheDriver.php

@@ -0,0 +1,56 @@
+<?php
+
+namespace Friendica\Core\Cache;
+
+use dba;
+use Friendica\Core\Cache;
+use Friendica\Database\DBM;
+use Friendica\Util\DateTimeFormat;
+
+/**
+ * Database Cache Driver
+ *
+ * @author Hypolite Petovan <mrpetovan@gmail.com>
+ */
+class DatabaseCacheDriver implements ICacheDriver
+{
+	public function get($key)
+	{
+		$cache = dba::selectFirst('cache', ['v'], ['`k` = ? AND `expires` >= NOW()`', $key]);
+
+		if (DBM::is_result($cache)) {
+			$cached = $cache['v'];
+			$value = @unserialize($cached);
+
+			// Only return a value if the serialized value is valid.
+			// We also check if the db entry is a serialized
+			// boolean 'false' value (which we want to return).
+			if ($cached === serialize(false) || $value !== false) {
+				return $value;
+			}
+		}
+
+		return null;
+	}
+
+	public function set($key, $value, $duration = Cache::MONTH)
+	{
+		$fields = [
+			'v'       => serialize($value),
+			'expires' => DateTimeFormat::utc('now + ' . Cache::duration($duration) . ' seconds'),
+			'updated' => DateTimeFormat::utcNow()
+		];
+
+		return dba::update('cache', $fields, ['k' => $key], true);
+	}
+
+	public function delete($key)
+	{
+		return dba::delete('cache', ['k' => $key]);
+	}
+
+	public function clear()
+	{
+		return dba::delete('cache', ['`expires` < NOW()']);
+	}
+}