The FieldErrorClass was not being set. [Fixes #30]

Allow models created without the 'errors' property to display errors.
Instead of getting the errors object and then checking the
property (`get('errors').get(property)`), just check the property 
(`get('errors.property')`).
Merge pull request #31 from diogomafra/errors-object

The FieldErrorClass was not being set. [Fixes #30]