Re-add Continuos deployment for automatic staging deployments

[epicallan]

We used to have an automated continuous deployment process but then disabled it coz i wasn't so happy with it.

We need to set up a new one.

• [ ] Set up a private docker registry
• [ ] push built images from circle-ci or travis to private docker registry
• [ ] Use Watchtower to auto deploy docker containers on image changes

We could actually add more steps on how we can improve this depending on time and priorities.