Added support for Traefik reverse-proxy

[johannesduesing]

Reason for this PR
As described in #24, we need to make instances deployed on the Docker host reachable from outside the host machine. We decided to make use of the reverse-proxy Traefik for this. Instances that have been deployed by the registry need to be labeled correctly so Traefik can process them.

Changes in this PR

• Deployed instances are now assigned a unique host string (using their unique id)
• The unique host is used as a label so that Traefik processes the instances after deployment
• The Instance class now contains an optional attribute traefikConfig which contains the unique host name and the Traefik proxy host
• The DAOs have been adapted so that the unique host string is stored correctly.
• There is now an GET /configuration endpoint which returns both the Docker HTTP host URI and the Traefik reverse-proxy URI
• Traefik is now set up during the installation script
• Readme and API specification have been updated accordingly