Change arguments of various functions for setting inertia matrices to const refs.
Cleanup related to ChBody::GetFrame_COG_to_abs() and ChBody::GetFrame_REF_to_abs().
Return the body lists of markers and forces as const references.

This actually prohibits changing the lists through these functions (which was previously "enforced" through a comment in the header file).
Remove old unused code.
Return const references to the lists of bodies and links of a ChAssembly.
More cleanup in ChBody (mostly const-related)
Cleanup of ChBodyDEM and ChBodyAuxRef.