Fixed/Implemented: replaced intval() by $app->functions->intval() in all interface functions due to big number problem in intval()

Added a new module called "domain". With this module you can manage all domains (web + mail). Per default this module is not active. To activate it, you have to change the System Interface Config -> domains -> use the domain module. You also have to activate the domain-module for the admin (and for every client if you want). Important: you can not use this module if you have reseller!

Removed some unmaintained tables and files and introduced the pre_update.sql script for sql commands to be run before an update.

- Changed shell of website linux user to /bin/false