CronSchedule timezone access

CronSchedule can be instantiated with a cron expression string, but there is no way to set a time zone. Specifically, the cron expression is not expected to contain time zone information; there is neither a CronSchedule constructor with a TimeZone argument nor with a CronExpression argument; and CronSchedule's CronExpression field is private.

The proposed solution is to add a constructor that will accept a TimeZone argument. The existing one-argument constructor would set the default time zone.