Docker/docker-compose enhancements

The following enhancements have been made to docker/docker-compose

* Fixed bug when building the image.
* docker-compose up starts the server
* Scaffolding inside the container respect the ownership of the files
outside it
* Volumes are tagged as 'delegated' in order to improve performance for
mac/windoze users.
* bundler stores packages in a volume. This whay new packages can be
added without rebuilding the image:

```bash
docker-compose run app bundle install
```

docker-compose.yml

@@ -1,31 +1,40 @@
-# service configuration for our database
-database:
+version: '3'
+services:
+  # service configuration for our database
+  database:
 
-  # use the preferred version of the official Postgres image
-  # see https://hub.docker.com/_/postgres/
-  image: postgres:9.4.5
+    # use the preferred version of the official Postgres image
+    # see https://hub.docker.com/_/postgres/
+    image: postgres:9.4.5
 
-  # persist the database between containers by storing it in a volume
-  volumes:
-    - docker-example-postgres:/var/lib/postgresql/data
+    # persist the database between containers by storing it in a volume
+    volumes:
+      - docker-example-postgres:/var/lib/postgresql/data
 
-# service configuration for our dockerized Rails app
-app:
+  # service configuration for our dockerized Rails app
+  app:
 
-  # use the Dockerfile next to this file
-  build: .
+    # use the Dockerfile next to this file
+    build: .
+    entrypoint: /usr/local/bin/entrypoint.sh
+    command: bundle exec rails s -p 3000 -b '0.0.0.0'
+    working_dir: /var/www/consul
 
-  # rely on the RAILS_ENV value of the host machine
-  # environment:
-  #RAILS_ENV: $RAILS_ENV
+    # rely on the RAILS_ENV value of the host machine
+    # environment:
+    #RAILS_ENV: $RAILS_ENV
 
-  # makes the app container aware of the DB container
-  links:
-    - database
+    # makes the app container aware of the DB container
+    depends_on:
+      - database
 
-  # expose the port we configured Unicorn to bind to
-  ports:
-    - "3000:3000"
-  # map our application source code, in full, to the application root of our container
-  volumes:
-    - .:/var/www/consul
+    # expose the port we configured Unicorn to bind to
+    ports:
+      - "3000:3000"
+    # map our application source code, in full, to the application root of our container
+    volumes:
+      - .:/var/www/consul:delegated
+      - bundle:/usr/local/bundle:delegated
+volumes:
+  docker-example-postgres: {}
+  bundle: {}