Fix: Ability load models saved using versions before 1.7

[tylernisonoff]

Fixes #1206

Uses the following defaults if they are not found in config_dict

defaults = {
    "id_col": "unique_id", 
    "time_col": "ds",
    "target_col": "y",
}

In 1.6.4, local_scaler_type and scalers_ were added to the dataset, so we check to see if those are set on the dataset, and use those as defaults if found. otherwise, we default to None

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[jmoralez]

Thanks!