[Alarm]: Implementation of Tizen alarm API.

This commit implements the Alarm API:
  https://developer.tizen.org/dev-guide/2.2.0/org.tizen.web.device.apireference/tizen/alarm.html

There is a known issue about repeat alarm: if the working system time zone is set to Daylight saving time like PDT or EDT, the repeat alarm finds 3600 seconds gap on the initial trigger time.

BUG=XWALK-428
ditto, var names and 4-space indent