Also do not print categories in quick print

* src/mail.h (updateCategories_o): Make public.
* src/ribbon-callbacks.cpp (print_decrypted): Remove categories
before print and add them after.

I think this is the more wanted behavior. If users used the
categories to mark mails as kind of "Top Secret" they should
just buy a stamp.

• GnuPG-Bug-Id: T4560