Cleanup of old code.
Merge branch 'develop' of https://github.com/projectchrono/chrono into develop
The .i files of the Python wrapper (unit_PYTHON) and the .h files must stay in sync.
Yesterday a commit broke the unit_PYTHON because the SWIG wrapper got a mismatch between ChQuaternion.h and ChQuaternion.i (those .i files are used to tell to SWIG what must be wrapped into a Python class/function). By the way, these .i files are most often simple .h references because SWIG can just parse the corresponding .h file and decide by himself, but for ChVector.h and ChQuaternion.h and few other classes, this was not possible so I had to override the funciton definitions line by line.
Therefore, when one changes something in the .h file for ChVector and ChQuaternion etc., he must also check to update the corresponding .i file if this is necessary.