Implemented checkboxes in Interface Config to enable showing/hiding the tabs Mail Filters, Autoresponders and Custom Rules for mailboxes.

See also http://www.howtoforge.com/forums/showthread.php?t=59539

Added: Changed idn function to support multi-line fields (like mail forward)

- need to have the pecl idn and intl modules installed
  or
- have the idna_convert class in the classes/idn/ path

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

Added Support for Sieve mail filtering language on dovecot servers.