Making C++/Python implementation of Dmp interchangeable

[stulp]

First implement these in Python

https://github.com/stulp/dmpbbo/blob/9cf0e5ed6911f76871ec883f9cb7a5c0c13e662e/src/dmp/Dmp.hpp#L64

https://github.com/stulp/dmpbbo/blob/9cf0e5ed6911f76871ec883f9cb7a5c0c13e662e/src/dmp/Dmp.hpp#L126

Check if same results

• Easy version: make a comparison as for the function approximators https://github.com/stulp/dmpbbo/blob/master/src/functionapproximators/tests/testTrainingCompareCppPython.py
• Hard version: make XML files readable/writable in Python
• Nice but impossible version: use JSON instead. Unfortunately, no good standard library JSON serialization for this in C++.

[stulp]

The "nice but impossible version" is now implemented in v2 of dmpbbo https://github.com/stulp/dmpbbo/tree/v2