Fix versions in docker compose

[lmarini]

For many of the services in docker compose we use latest. Depending on the experience of the user and the environment they are in (for example no access to the internet), this can create situations when they are running older versions of some services (for example extractors) and can potentially get errors. Should we drop latest and fix it specific versions?

[robkooper]

Just looking at this, the only one that is not specified is rabbitmq.
traefik = 1.7 (should really be upgraded)
mongo = 3.6
clowder = in .env, defaults to latest
clowder-monitor should be the same as clowder
elasticsearch = latest, should be 1.2

We should pin the extractors to a specific version and not just latest. Let me know if that is what you wanted.