[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
Show the code should like, should be more clear.
```
namespace {

const char kAlarmInfoKey[] = "service.extra.alarm";
const char kHostAppIdKey[] = "service.extra.hostappid";

bool AlarmIterateCallback(int id, void* userdata) {
  std::vector<int>* ids = reinterpret_cast<std::vector<int>*>(userdata);
  ids->push_back(id);
  return true;
}

}  // namespace