Getting ConfigurationSpace should be a class method

[eddiebergman]

Currently the test code has a lot of creating objects just to get the configuration space and then setting hyperparameters.

pipeline = SimpleRegressionPipeline(dataset_properties=dataset_properties)
cs = pipeline.get_hyperparameter_search_space()

# ...later
config = cs.sample_configuration()
config._populate_values()

cls = SimpleRegressionPipeline(
    random_state=1,
    dataset_properties=dataset_properties
)
cls.set_hyperparameters(config)

Seeing as the configuration space doesn't rely on anything except the dataset_properties set through the constructor and whatever the constructor can deduce from this, it would be more syntactically clear to move get_hyperparameters_search_space() to be a @classmethod

[mfeurer]

The function has some side-effects (setting attributes on self), but this could definitely be refactored.

[eddiebergman]

Good to note, considering the object gets constructed and then thrown away, I feel these side-effects are probably easy enough to fix.