Create SafeXGBoostClassifier class

[jim-smith]

Sub-class of safeModelClassifier:

• needs parameter recommendations. from @rpreen 's results
• ideally should implement the k-anonymity reporting functionality
  • but recognise I don't know if their forest/tree structure is the same as sklearn's Tree
• need to identify what should go in the "examine separately " functionality
• documentation of base package here: https://xgboost.readthedocs.io/en/latest/python/index.html