check(model, prop) {
        this.set('passed', true);

        if (prop && this[prop]) {
            this[prop](model);
        } else {
            this.properties.forEach((property) => {
                if (this[property]) {
                    this[property](model);
                }
            });
        }
        return this.passed;
    }
When passed a model and (optionally) a property name,
checks it against a list of validation functions
@param  {Ember.Object} model Model to validate
@param  {string} prop  Property name to check
@return {boolean}      True if the model passed all (or one) validation(s),
                       false if not