[WIP] Refactoring: Python interface

[alejandrosame]

Description

Now it's possible to do

from pydp.algorithms.laplacian import Count
count = Count(epsilon=1)
count.result([1,1,1,1])

In order to avoid confusion, I also rename pydp.so to _pydp.so as it seems to be common practice when integrating Python code with C/C++ extensions.

How has this been tested?

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Checklist

• I have followed the Contribution Guidelines and Code of Conduct
• I have commented my code following the OpenMined Styleguide
• I have labeled this PR with the relevant Type labels
• My changes are covered by tests