refactoring:
removed static self-registration blocks from GregorianCalendarManager and JavaDateCalendarManager
changed CalendarManager to abstract
moved a few common methods to CalendarManager
expanded CalendarFactory:
now responsible for registering instances of CalendarManager with itself
now responsible for loading XML Calendars and initializing and registering them
Calendar:
removed JAXB afterUnmarshal
changed CalendarManager Version Identifier back to 8 bits length