Major refactor to error retrieval methods and class names

You no longer use the method .getMsgFor() to retrieve messages or
.getError() to retrieve the error. All errors now exist in an
instance of Ember.Validator.Result.

Retrieve errors just with it's path,
 person.validate().get('error.name') will get the name error object.

Retrieve messages with person.validate().get('error.name.message').

This was done to help with views trying to bind to the error property
rather than the former result object.

Class name changes are as follows:
Ember.Validator.Results -> Ember.Validator.Result
Ember.Validator.Result -> Ember.Validator.Error