Implement configuration via container extensions

This means you can configure the bundle settings without extending
the base controller class.

For example: you can add these settings to your config.yml file

```yaml
c33s_static_pages:
    content_bundle: MyBundle
    content_dir:    Pages
```

You can either look at the Configuration class or run
`app/console config:dump-reference c33s_static_pages` (after pulling) to see
a list of all current configuration parameters.