remove enumitem from beamer org export

Signed-off-by: Micky Ching <mickyching@gmail.com>
modify font setting

add function toggle use bigger Chinese font.
org export font use WenQuanYi Micro Hei for Chinese mono,
English mono is using Fantasque Sans Mono.

Signed-off-by: Micky Ching <mickyching@gmail.com>