[NFY] Feature/data bag item encryption

Feature description: If a data bag item is encrypted, its encrypted attributes are not shown and a key needs to be pasted or uploaded in order to access decrypted data. This feature will not available for users of Chef 10.x - in their case, the encryption will not be recognized and they should simply see a list of encrypted attributes.

(This can be merged only after #35)

Unfortunately, I have a problem with the fixtures. Running 'features/data_bag_item.feature', where a key to view decrypted attributes is provided, results in getting a `NotImplementedError - Currently decrypting only version 0 & 1 databags are supported`. I wasn't able to reproduce this error when actually using the app. The encrypted data bag item used for testing was created using knife; decrypting using both knife and chef browser worked. Here's the knife output:

```
$ knife data bag show some-data-bag secret-data-bag-item
id:       secret-data-bag-item
login:
  cipher:         aes-256-cbc
  encrypted_data: k/cjNY+0ORupMS0Ml0CA7hVaw64YdUeZfDjulKjwT7E=
  
  iv:             WeC/BubdLPQ7R6YIovtFDQ==
  
  version:        1
password:
  cipher:         aes-256-cbc
  encrypted_data: HpG5sXDexINdS75rysOayJ122f84amKeTgX6g3EgeFE=
  
  iv:             Oi7Y6mSpJyXiN7rgjNx0Ow==
  
  version:        1

$ knife data bag show some-data-bag secret-data-bag-item --secret-file encrypted_data_bag_secret
id:       secret-data-bag-item
login:    admin
password: admin
```

If I understand correctly, it's version 1, which ought to be supported by Ridley. Or am I wrong? This is something that, unfortunately, I am not able to grasp.