#636 add two new APIs for PacoNotificationManager
#636 add three new APIs for PacoScheduler
#636 add new APIs to PacoExperimentSchedule and PacoExperimentDefinition
#636 add new APIs to refresh experiments after definition gets refreshed successfully
#636 after definitions get refreshed successfully, we clean expired notifications, and refresh experiments and notification system according,
instead of deleting all running experiments and shut down notification system.