Docker cleanups

- Start the docker dev-env osem on port 3000. Just as our documentation says
  and how we do it in vagrant.
- hardcode CONTAINER_USERID so you don't have to have an
  docker-compose.override.yml if your UID is 1000.
- Rename web service/container to osem for clarity in the logs
- Keep assets also in a volume in production

bin/osem-init.sh

@@ -6,4 +6,4 @@ bundle check || bundle install --jobs=3 --retry=3
 # Setup the app if it isn't already setup
 bundle exec rake setup:bootstrap
 # Start the app
-foreman start
+foreman start -p 3000