Fixed issue with shell user creation due to missing parent user and group values in shell_user database records.

- Use it like $app->conf('yourpluginname', 'config-key', 'value')
- omit the value to read the config value, provide it to set the value

Changed mode of web folder from 0710 to 0711 to make it comaptibe with servers that use NFS for /var/www.

- database users
- email forwarders and aliases
- clients