public function add($identifier, array $configuration)
    {
        $presets = $this->loadPresets();
        if (!empty($presets[$identifier])) {
            throw new Exception('Preset exists already', 1410552459);
        }
        if (empty($configuration)) {
            throw new Exception('Empty configuration is not allowed', 1410595656);
        }
        $presets[$identifier] = $configuration;
        ksort($presets);
        $this->savePresets($presets, 'Adds preset with identifier "' . $identifier . '"');
    }