- Improved installer and updater for multiserver mode. Modules and plugins were only configured if the selected service is available on the server.

- updated the debian installation instructions

- added server module for firewall and database.

Moved server modules and plugins to new directory and updated the installer to create the symlinks for the modules and plugins from *-available to *-enabled directory.
Fixed a typo in mailfilter template.

- improved several functions in site module
- added server classes to restart services