[RTR] Preparing the work for refactoring external forces

[Ipuch]

• Linked issue related to your pull request using :

• External Force feature need to be refactored #112
• Inverse Dynamics #70
• Inverse Dynamics validation #87
• Creating a ExternalForce object from c3d force plateform #106
• [WIP] Example of inverse dynamic #107

• Used the tag [WIP] or [RTR] for on-going changes, or for ready to review
• Did you write new tests to cover your changes?
• Did you write a proper documentation (docstrings and ReadMe)
• Please black your code black . -l120

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[qlty-cloud-legacy]

Code Climate has analyzed commit 31219df and detected 4 issues on this pull request.

Here's the issue category breakdown:

Category	Count
Complexity	4

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