Changelog:
* Update the unittests, improve code coverage
* Equal operator overload for Link, Joint and CameraResolution (update) classes
* Update for internal depth camera computation, fixing issue 24
* Catch exceptions when stopping the simulation, fixing issue 11
* Faster computation for getAnglesPosition (see attached figure)
* Additional resources refactoring: installation process for the URDFs and meshes
* Update the CI, remove Python 3.4 (EOL), add Python 3.6, 3.7 and 3.8
![anglepos_computing](https://user-images.githubusercontent.com/11226450/73089855-69138880-3ed7-11ea-80c4-b67ebadb3112.png)