ValidationError messages include field value

I modified the formatErrors() function to include the current value of the fields which have failed validation.

The format looks like this:

```
The `Person` instance is not valid. Details: `id: 123456` can\'t be set.
```

Please let me know if that format is good, and I will update the test expectations to match.
@bitmage , I think this shouldn't be logged by default to server console.