Fixed: FS#3350 - [Dovecot] Warning: mysql: Query failed, retrying: Unknown column 'filter' in 'where clause'

Changed cron_daily.php to avoid some php notices.

- Implemented FS#3308 - PATH placeholder in directive snippets (placeholder is named {DOCROOT}, like for nginx).

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

- database users
- email forwarders and aliases
- clients

- Added email message templates.