(holidays): Move custom groups here from calendar.el.

(holidays): Move custom groups here from calendar.el.
(holiday-general-holidays, holiday-oriental-holidays)
(holiday-local-holidays, holiday-other-holidays, hebrew-holidays-1)
(hebrew-holidays-2, hebrew-holidays-3, hebrew-holidays-4)
(holiday-hebrew-holidays, holiday-christian-holidays)
(holiday-islamic-holidays, holiday-bahai-holidays)
(holiday-solar-holidays, calendar-holidays): Move here from calendar.el.