Use more environment variables for server configuration

[HomereB]

Before pull request #20 is merged, we should try to add more variable to the .env file to make the demo setup less tedious.

• within the docker-compose.yml file : within the udviz service section, the IP address of the host in the command line should be a .env variable command : npm start -- --host=<host-IP-address> --port=${UD_VIZ_PORT}
• within the ud-viz-context/DemoConfigData.json file : the "geoserver" line should be configured through the .env file, meaning we should add a variable for the domain name. "http://<fully-qualified-domain-name-of-server>:<chosen-geoserver-port>/geoserver/cite/ows?"

[HomereB]

• command line changed and no longer requires the host argument, and port is now configured in the .env file and passed to the dockerfile
• both server FQDN and port of the geoserver line in the config file are now configured using the .env file

[HomereB]

Demo finalized and dockers can now be configured through .env file