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

docker-compose.yml.dev-example

@@ -5,13 +5,15 @@ services:
     image: postgres
     environment:
       PGDATA: /var/lib/postgresql/data/pgdata
-  web:
-    build: .
-    # env_file: dotenv.example
+  osem:
+    build:
+      context: .
+      args:
+        CONTAINER_USERID: 1000
     command: /osem/bin/osem-init.sh 
     depends_on:
       - database
     ports:
-      - 5000:5000
+      - 3000:3000
     volumes:
       - .:/osem