New global option to grant reseller users access to the options (advanced) tab in web domains and vhost subdomains

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!

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Changed database prefix to client ID instead of client name to better use the limited username length of mysql.

- Updated the user and database prefixes to use this storage.