Changes:
- Removed all CalendarData related files (part of the process of replacing it with individual components)
- Commented out references to CalendarData in EventEditor
- Removed unnecessary variables from Event (year, month, etc. when we have startDate and endDate)
- Added some required methods to ICalendarEntry and implemented them in Event
- Put placeholder methods required by ICalendarEntry in Commitment
- Completely rewrote EventTest to better test rewritten Event class
- Removed references to CalendarData in ManagerLayer