Shortened the names.
Better conversions.
A little more tests.

--HG--
rename : dates/src/main/scala/org/podval/calendar/dates/GregorianCalendar.scala => dates/src/main/scala/org/podval/calendar/dates/Gregorian.scala
rename : dates/src/main/scala/org/podval/calendar/dates/GregorianCalendarHelper.scala => dates/src/main/scala/org/podval/calendar/dates/GregorianHelper.scala
rename : dates/src/main/scala/org/podval/calendar/dates/CalendarHelper.scala => dates/src/main/scala/org/podval/calendar/dates/Helper.scala
rename : dates/src/main/scala/org/podval/calendar/dates/JewishCalendarHelper.scala => dates/src/main/scala/org/podval/calendar/dates/JewishHelper.scala