adding Debian copyright file

Bareos license (AGPL3 with exceptions) is described in the file "LICENSE"
(based on the Bacula LICENSE file).
However, Debian require license information in a specific file and format (debian/copyright).
This patch adds this file and also includes it to the bareos-common RPM.

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

remove some Debian lintian warnings.

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