RESTAdapter : Convert errors object returned with a 422 in an Ember Object
Use App.Model.total to store the total number of elements given in the meta data of the request
Store the total number of elements given in the meta data of each request into `App.modelCount`
RESTAdapter : Improve errors 422 (validation) for embedded records

When an error 422 is received, all embedded records will be send to the invalid state
When an invalid record is modified, it will became valid. His parents will became valid too if all of their embedded records are valid.