Added CalendarStructure classes

Data structures to allow us to store all events, commitments, etc.
associated with a calendar in one place. Also added a PersonalCalendar
class which has info about the user it belongs to, and a TeamCalendar
class which has info about the project it belongs to.
Calendar Model and TeamCalendarEntityManager

Changed CalendarStructure to CalendarModel and made a
TeamCalendarEntityManager. Wrote toJSON and fromJSON functions for
TeamCalendar, and stubbed them out for PersonalCalendar. Made changes to
the ManagerLayer to add the TeamCalendarEntityManager as the tutorial in
the wiki described, but I am still getting errors there.
TeamCalendarEntityManager will still need an update function at the
least, and the functions that we don't want to be used will need to
throw exceptions.
Fixing merge conflict

I can't push any changes because of this merge conflict in CalendarItem.
Unfortunately I messed up and picked the wrong version to commit. So I
will fix it again and make another commit to update this file.