Set to default new logic. Add cleartext password hash implementation.

TODO:
- add new implementation of the rest of currently supported hashes
- create update.php changing hash names in the config

lib/HashAlgorithm/Cleartext.php

@@ -0,0 +1,75 @@
+<?php
+/**
+ * Nextcloud - user_sql
+ * Copyright (C) 2012-2018 Andreas Böhler <dev (at) aboehler (dot) at>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+namespace OCA\user_sql\HashAlgorithm;
+
+/**
+ * Cleartext password hash implementation.
+ * @author Marcin Łojewski <dev@mlojewski.me>
+ */
+class Cleartext implements HashAlgorithm
+{
+    /**
+     * @var Cleartext
+     */
+    private static $instance;
+
+    private function __construct()
+    {
+    }
+
+    /**
+     * @return Cleartext
+     */
+    public static function getInstance()
+    {
+        if (self::$instance === null) {
+            self::$instance = new Cleartext();
+        }
+        return self::$instance;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function getVisibleName()
+    {
+        return "Cleartext";
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function getPasswordHash($password)
+    {
+        return $password;
+    }
+
+    /**
+     * @inheritdoc
+     */
+    public function checkPassword($password, $dbHash)
+    {
+        return $password === $dbHash;
+    }
+
+    private function __clone()
+    {
+    }
+}