Fix #10 Fix #17 - Add toggles to enable and disable operations

This fix adds a new group of settings for enabling or disabling operations:

```yaml
  allow:
    
    # If false, throw 403 for GET builds/(:id) and GET builds/(:id)/metadata 
    # requests.
    builds_metadata: true
    
    # If false, throw 403 for GET builds/(:id)/raw/.. request.
    builds_raw: true
    
    # If false, throw 403 for GET builds/(:id)/zip request.
    builds_zip: true
    
    # If false, throw 403 for GET jobs/create and POST api/jobs requests.
    jobs_create: true
    
    # If false, throw 403 for GET api/jobs/(:id)/delete request.
    jobs_delete: true
    
    # If false, throw 403 for GET api/jobs/(:id) request.
    jobs_status: true
```

This will help with making it easy to enable and disable features such as in a split build environment or if the server is used only to distribute zips but not provide raw contents.