Add PMD's CouplingBetweenObjects scanner

[jimbethancourt]

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Add PMD's CouplingBetweenObjects scanner to identify classes that have a strong likelihood of being involved in a dependency cycle. Zazworka et. al. found that classes involved in dependency cycles had the highest likelihood of change proneness. Performing a CBO scan should enable an O(n) time scan while providing approximate results that can still be ordered against relative churn and allow for approximate prioritization and help developers identify a good place to start.