Moved calculations to helpers.

--HG--
rename : dates/src/main/scala/org/podval/calendar/dates/GregorianCalendarConstants.scala => dates/src/main/scala/org/podval/calendar/dates/GregorianCalendarHelper.scala
rename : dates/src/main/scala/org/podval/calendar/dates/JewishCalendarConstants.scala => dates/src/main/scala/org/podval/calendar/dates/JewishCalendarHelper.scala