org: modify beamer theme

decrease margin size, smaller source code size.

Signed-off-by: Micky Ching <mickyching@gmail.com>
add language environment setting

Signed-off-by: Micky Ching <mickyching@gmail.com>
add user name and email settings

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

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