Executing defaults function
i-model__field.getDefault() executes default if it's a function
i-model__field_type_model and i-model__field_type_models-list
.isChanged() implementation
Context of default fn changed to model not field
Merge pull request #114 from verkholantsev/functions_as_defaults

Get default value for field as function execution result
Merge pull request #113 from verkholantsev/is_changed_for_models_and_models-list

implement isChanged method for field type model and models-list