Add Python Wrapper

[goodwillpunning]

Fixes [#3]. This commit adds a Python Wrapper to the DataFrame Rules Engine project.

In particular, this commit adds the following functionality in Python:

• Define a Rule using a String LOV in Python
• Define a Rule using an Expression in Python, including User-Defined Functions
• Define a Rule using a Bounds expression in Python
• Define a Rule using a MinMaxDef expression in Python

Furthermore, this commit also adds 2 new functions to the Scala RuleSet class for getting the summary and complete validation reports:

• getCompleteReport()
• getSummaryReport()

[codecov[bot]]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (ef9b9fa) 87.50% compared to head (cb968bd) 86.47%.

Files	Patch %	Lines
...scala/com/databricks/labs/validation/RuleSet.scala	80.00%	3 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #37      +/-   ##
==========================================
- Coverage   87.50%   86.47%   -1.03%     
==========================================
  Files           5        5              
  Lines         168      170       +2     
  Branches        3        2       -1     
==========================================
  Hits          147      147              
- Misses         21       23       +2     

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[CLAassistant]

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