style(AcademicCalendar): clean up instance variables, make most private, remove unused ones
style(AcademicCalendar): clean up instance variables, make most private, remove unused ones

There were instance variables used *only* inside AcademicCalendar methods which were unnecessarily
public. Also, the `server` instance variable was found to be never used after the constructor.
This prepends an underscore to those variables, and also removes the `server` instance variable.

BREAKING CHANGE: instance variable `server` has been removed from class AcademicCalendar.
Justification: The value of `server` is used only in the initialization of the LDAP server (in the AcademicCalendar constructor), and never again.
Migration: None - there was no code using `self.server`.

rosshamish/classtime,ahoskins/Winston,rosshamish/classtime,ahoskins/Winston