Allow save to save to string (referring to environment)

[surister]

def save(cls,
         to: 'Storage' = None,
         format: DataFormat = None,
         table_name: str = None,
         environment: str = None,
         **kwargs):

to accepts only a Storage, e.g. Storage.env1, it can sometimes be useful to be able to just specify the storage name, e.g.

Model.save(to='environ1')