Fixed some charset issues

- Fixed files with mixed character set or invalid CP949 characters.
- Uncommented '#music' script in the_sign_quest.txt (now the
  soundeffect filename should be fixed).
- Added a note to the header of CP949 files not to read or save them as
  UTF8, since it'd break their encoding. It should be safe enough to
  read them as EUC-KR if your text editor doesn't offer CP949 as an
  option.
- Added FIXME notes about untranslated strings in assassin_skills.txt
  and WolfchevLaboratory.txt.

Signed-off-by: Haru <haru@dotalux.com>