Debian packaging: Address #10 #11 #12 and #13

• Add Debian-specific version of service unit file
• Add main package to debian/control
• Provide *.install, *.docs for both packages
• Let dh_systemd (and "dh --with systemd") handle pre/post scripts

Relates #10 (closed), relates #11 (closed), closes #12 (closed), closes #13 (closed)

config/gwdatafind-server.service

@@ -7,7 +7,7 @@ After=network.target
 [Service]
 Type=simple
 User=gwdatafind
-ExecStart=/usr/bin/gunicorn-3 --config /usr/share/gwdatafind-server/gunicorn.conf.py "gwdatafind_server:create_app()"
+ExecStart=/usr/bin/python3 -m gunicorn.app.wsgiapp --config /usr/share/gwdatafind-server/gunicorn.conf.py "gwdatafind_server:create_app()"
 ExecStop=/bin/kill -s TERM $MAINPID
 NoNewPrivileges=true
 PrivateTmp=true