Fix #14 - Make Docker more flexible

* Expose Volume so Policies can be injected
* Remove hard-coded 8080 port and replace with optional `ENV` parameter in case port 8080 is in use. Port 8080 remains the default.

docker/Dockerfile

@@ -68,8 +68,10 @@ RUN curl --silent --output authzforce-ce-server.deb --location $AUTHZFORCE_SERVE
  rm -rf /opt/authzforce-ce-server/data/domains/* && \
  rm -rf /root/authzforce && \
  rm -f authzforce-ce-server.deb
+
+VOLUME /opt/authzforce-ce-server/data
+
 CMD ["catalina.sh", "run"]
 
 ### Exposed ports
-# - App server
-EXPOSE 8080
+EXPOSE ${AUTHZFORCE_PORT:-8080}