Issue #216 : add unit tests, fix bugs
Issue #216 : implemented unit tests for notification manager and modify code accordingly
Issue #216 : implement an unit test and modify code accordingly
Issue #216 : add a new API to cancel all notifications for an experiment
Issue #216 : add new APIs to save and load notifications, add unit tests.
Issue #216 : code refactor
Issue #216 : code refactor
Issue #216 : API improvement and update unit tests accordingly