PostgreSQL 11 support + Dockerfile improvements
In this PR:
- PostgreSQL 11 support.
- Extra software (nodejs, etc) removed fron Dockerfile.
- No plsh for Postgres 11 (the package doesn't exist yet).
- Performance-related settings removed from "tweaking" Postgres config files.
- README for docker updated.
- pgBadger is v10.1 now, not the lastest dev version from master branch.
- New docker image location: https://hub.docker.com/r/postgresmen/postgres-nancy/tags/