Feature/expose pdo transactions api

[kvydiuk]

Expose PDO transactions API so it can be used for grouping a series of database operations.
It ensures data integrity by guaranteeing that all operations either succeed completely or fail entirely, leaving the database unchanged.

Usage example:

try {
            $sql = new sql();
            $sql->getDbClient()->DB()->beginTransaction();

            $sql->insert('vudoo_affiliates')
                ->field('integration_request_id')->value(93)
                ->field('token_id')->value(0)
                ->field('name')->value(sprintf('af_%d', time()))
                ->field('code')->value(sprintf('cd_%d', time()))
            ->writeEntry();

            $sql->insert('vudoo_affiliates')
                ->field('integration_request_id')->value(93)
                ->field('token_id')->value(0)
                ->field('name')->value(sprintf('af_%d', time() + 1))
                ->field('code')->value(sprintf('cd_%d', time() + 1))
                ->writeEntry();

            $sql->getDbClient()->DB()->commit();
        } catch (\Exception $e) {
            $sql->getDbClient()->DB()->rollBack();
        }

We can also improve DB client declared in the platform codebase with the support of transaction methods to simplify usage:

$sql->beginTransaction();

instead of

$sql->getDbClient()->DB()->beginTransaction();