Merge all configuration files of 2-advanced

All configuration files (db.php,  email_passwordreset.php, email_verification.php, email.php, hashing.php) have been merged in only ONE configuration file: config.php

The main files (edit.php,  index.php, password_reset.php, register.php) have been updated to include now only the new config.php

Old config files have been deleted to keep only config.php