Support to Korean Traditional Calendar, Dan-gi(단기/檀紀) Calendar

The era name, Dangi(단기,檀紀) originating from the foundation of Gojoseon[고조선/古朝鮮] is also widely used in Korea as an indication of long civilization of Korea.

Full name: `Dangun-giwon (단군기원, 檀君紀元 "First Age of Lord Dangun")`

Abbreviation Name: `Dangi(단기,檀紀)`

The Dangi Calendar measures years from the ancient founding of Korea in 2333 B.C.

Reference. ICU Library
ICU library support Dangi Calendar.
ICU4C 50 http://bugs.icu-project.org/trac/ticket/9255
ICU4J 51 http://bugs.icu-project.org/trac/ticket/9616

Change-Id: I490b8b288c68f498eb29d4fcc73251cbef3ac6d4
Reviewed-on: https://gerrit.libreoffice.org/72943
Tested-by: Jenkins
Reviewed-by: Eike Rathke <erack@redhat.com>