moved bsmtp from bareos-director to bareos-common

The program bsmtp is used by bareos-dir but also by btraceback.
Therefore it is moved to the bareos-common package.

Fixes #251: /usr/sbin/bsmtp is part of the director but is needed from btraceback

Signed-off-by: Marco van Wieringen <marco.van.wieringen@bareos.com>