refactoring of crypto flags
The implementation of LibBalsaMessage::prot_state and LibBalsaMessage::gpg_mode was confusing (see the discussion at #70 (comment 1410666) ff.). This branch unifies them, and shifts implementations of some methods to more appropriate places:
- replace gpg_mode and prot_state by a common guint crypt_mode field
- move the defines for the crypt_mode field to message.h, fix naming for S/MIME
- rename getter/setter for crypt_mode
- separate the flag to always trust keys into a separate field, and add getter/setter for it
- shift the method to get a body's signature state to body.[hc]
Signed-off-by: Albrecht Dreß albrecht.dress@netcologne.de