Easily create deb/rpm (with systemd unit file)

You can now use 'sbt debian:packageBin' and 'sbt rpm:packageBin'
This create a 'cerebro' user
This also add a /var/lib/cerebro dir owned by cerebro (to put the db)

Signed-off-by: Etienne Champetier <etienne.champetier@anevia.com>