Add a draft implementation of the -d, --decrypt command (which is
used both to decrypt and/or to verify). The core functionality is
there, but the UI could probably be better, both in terms of
aesthetics and in terms of informations shown about the decrypted
or verified file.
Disable the OK/Confirm button until a workable action (sign and/or
encrypt) has been defined by the user. Also only enable the
detached signature button when it makes sense, i.e. when signing
is enabled and encryption is disabled.
Refactor the code to get rid of the yki_ctx_t structure, which is
replaced by a yki_encrypt_data_t structure that is internal to
the encrypt module.