Write simple cron scheduler

http://pmkathiria.blogspot.com/2013/06/how-to-write-simplecron-scheduler-in.html

http://www.liferay.com/community/forums/-/message_boards/message/25000365

http://itsliferay.blogspot.com/2012/08/implement-scheduler-in-liferay-61.html

http://www.quartz-scheduler.org/documentation/quartz-1.x/tutorials/crontrigger

http://www.cronmaker.com/

https://www.liferay.com/community/forums/-/message_boards/message/5248713