FEAT #1810 manage crontab in interface (only linux)

notifications/trunk/batch/config/config.xml.default

notifications/trunk/class/class_schedule_notifications.php

notifications/trunk/class/notifications_controler.php

notifications/trunk/create_notif_script.php

notifications/trunk/js/functions.js

notifications/trunk/lang/en.php

notifications/trunk/lang/fr.php

notifications/trunk/manage_notifications.php

notifications/trunk/manage_notifications_controler.php

notifications/trunk/schedule_notifications.php

notifications/trunk/schedule_notifications_controler.php