ChQuaternion<Real> GetInverse() const       throws an error when used outside of the ChronoEngine build:
IntelliSense: the object has type qualifiers that are not compatible with the member function
Length() functions in ChQuaternion.h should also be 'const' functions.
Merge pull request #15 from jcmadsen/develop

ChQuaternion<Real> GetInverse() const       throws an error when used outside of the ChronoEngine build