Add standard and custom metrics to metrics_dict

def calculate_metrics(self, model, train_loader, valid_loader, metrics_dict):
        """Add standard and custom metrics to metrics_dict"""
        # Check whether or not it's time for validation as well
        self.log_count += 1
        log_valid = (
            valid_loader is not None
            and self.valid_every_X
            and not (self.log_count % self.valid_every_X)
        )

        metrics_dict = {}

        # Calculate custom metrics
        if self.config["log_train_metrics_func"] is not None:
            func = self.config["log_train_metrics_func"]
            func_list = func if isinstance(func, list) else [func]
            for func in func_list:
                metrics_dict = self._calculate_custom_metrics(
                    model, train_loader, func, metrics_dict, split="train"
                )
        if self.config["log_valid_metrics_func"] is not None and log_valid:
            func = self.config["log_valid_metrics_func"]
            func_list = func if isinstance(func, list) else [func]
            for func in func_list:
                metrics_dict = self._calculate_custom_metrics(
                    model, valid_loader, func, metrics_dict, split="valid"
                )

        # Calculate standard metrics
        metrics_dict = self._calculate_standard_metrics(
            model, train_loader, self.log_train_metrics, metrics_dict, "train"
        )

        if log_valid:
            metrics_dict = self._calculate_standard_metrics(
                model, valid_loader, self.log_valid_metrics, metrics_dict, "valid"
            )

        return metrics_dict