Korean language update

inc/lang/ko/install.html

inc/lang/ko/lang.php

inc/lang/ko/mailtext.txt

inc/lang/ko/preview.txt

inc/lang/ko/showrev.txt

inc/lang/ko/updateprofile.txt

lib/plugins/acl/lang/ko/help.txt

lib/plugins/acl/lang/ko/lang.php

lib/plugins/config/lang/ko/intro.txt

lib/plugins/config/lang/ko/lang.php

lib/plugins/popularity/lang/ko/intro.txt

lib/plugins/usermanager/lang/ko/edit.txt

lib/plugins/usermanager/lang/ko/lang.php