Adding KNNClassificationDeciders to ProgLearn

[david-z-shi]

Is your feature request related to a problem? Please describe.
An extension to issue #5, transferring the KNNDecider idea to the classification setting.

Describe the solution you'd like
Create a decider with the following properties:

• Create a list of KNNClassifiers from sklearn for each bag
• The features to the KNNClassifier are the posterior probabilities from each transformer and each class.
• Infer the hard class assignments from these KNNClassifiers from each bag.
• Normalize and use the argmax of the results.

Describe alternatives you've considered

Additional context (e.g. screenshots)

[david-z-shi]

@jdey4 Can I be assigned to this