Updated DBDAO class:
    * Constructor made private
    * Added static function makeFromDB() to create DB instance from DB object
    * Added static function makeFromSettings() to create DB instance from database configuration section in settings.yml file
    * Added static function makeFromConfigurationFiles() to create DB instance from database configuration section in provided yaml configuration files
    * Added static function makeFromConfigurationArray() to create DB instance from assoc. array containing database configuration settings