Clean up CzmlPrimaryObject

There are methods in CzmlPrimaryObject that, I think, should not belong to this interface.

Dates:

• Should be handled by static functions in a separate class DateUtils
• Names should be reduced:
  • absoluteDateToJulianDateOriginDelta: secondsSinceJulianEpoch?
  • absoluteDateToJulianDate → toJulianDate ou createJulianDate: the fact that we have a JulianDate in input is in the signature
    • reduce the code in this one
  • absoluteDatelistToJulianDateList → toJulianDates ou createJulianDates
  • julianDateToAbsoluteDate et julianDateListToAbsoluteDateList: idem
  • (not used)julienDateListToTimeIntervals: createTimeIntervals

sortingListList(List): to be put in the concerned classes as private method, not at the interface level