added settings, removed hardcoded path, arg'd script

alas it is broken:

sh: 1:
/home/xbian/.xbmc/addons/script.service.dlmanager/transmission_limit.sh:
not found

Yet:

$ ls -la
/home/xbian/.xbmc/addons/script.service.dlmanager/transmission_limit.sh
-rwxr--r-- 1 xbian xbian 749 Mar  1 13:29
/home/xbian/.xbmc/addons/script.service.dlmanager/transmission_limit.sh