Implemented suggestion "Script Command to block commands" http://rathena.org/board/topic/88888-script-command-to-block-commands/
-- Added new script commands: 'enable_command', 'disable_command'
-- Added new config 'atcommand_enable_npc' at conf/battle/gm.conf
-- Thank Kichi for the patch file

Signed-off-by: Cydh Ramdh <house.bad@gmail.com>