Execute Python code on the fly and display results in Superset visualizations

[charithmadhuranga]

Analytics Extension implementation that expands superset's capabilities by allowing users to execute Python scripts and saved functions via superset

usecase

Use Python for data cleaning and predictive algorithms inside superset.

benifit

Allows authoring calculated fields in Python.

This idea was taken from tableau's Tabpy framework

https://github.com/tableau/TabPy

[crazyproger]

This is the thing why we can't move from Zeppelin to Superset - lack of process-data-in-the-middle feature in superset.