several issues in DvDateTime

[Sergio Miranda Freire]

Argument magnitudeStatus is missing in the initializer and in the call to the superclass initializer.
magnitude is an derived attribute, so it does not need to appear as an argument in the initializer.

DvDate inherits from DvAbsoluteQuantity and ISO8601DateTime (support package). So it is necessary to implement all methods of both classes, namely:
      add, subtract, diff, compare, isStrictlyComparableTo (DvAbsoluteQuantity)
     asString, year, month, day, hour, minute, second, monthUnknown, dayUnknown, hourUnknown, minuteUnknown, fractionalSecond, hasFractionalSecond, timezone, secondUnknown isPartial, isExtended, isValidISO8601DateTime, isDecimalSignComma (ISO8601DateTime) and enforce the invariants:
Year_valid: valid_year(year)
Month_valid: valid_month(month)
Day_valid: valid_day(year, month, day)
Invariants
Hour_valid: valid_hour(hour, minute, second)
Minute_valid: not minute_unknown implies valid_minute(minute)
Second_valid: not second_unknown implies valid_second(second)
Fractional_second_valid: has_fractional_second implies (not second_unknown
and valid_fractional_second(fractional_second))
Partial_validity_year: not month_unknown
Partial_validity_month: not month_unknown
Partial_validity_day: not day_unknown
Partial_validity_hour: not hour_unknown
Partial_validity_minute: minute_unknown implies second_unknown