Tidy up old name references, and rename cd submodule to dd

[ascillitoe]

The drift detection submodule was named cd for "concept drift". We should rename it to dd for drift detection. There are also a number of items scattered around that could be renamed in a similar fasion. For example, in alibi_detect.base, concept_drift_dict should be renamed drift_prediction_dict, and "outlier" below needs removing:

class BaseDetector(ABC):
    """ Base class for outlier detection algorithms. """

@arnaudvl noted that we could also make all our detectors accessible one level higher e.g. from alibi_detect import MMDDrift since they mostly have "Drift" or "Outlier" in their names (we might want to rename adversarial detectors e.g. ModelDistillation in this case).