Docker cleanups

- Put docker-compose.yml into version control, no need to make this an example
  file and complicate things.
- 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
- warn a bit more prominently about docker-compose.override.yml

bin/osem-init.sh

@@ -1,3 +1,5 @@
 #!/bin/bash
+# Setup the app if it isn't already setup
 bundle exec rake setup:bootstrap
-foreman start
+# Start the app
+foreman start -p 3000