SofaBaseMechanics: use virtual inheritance for a component
SofaBaseMechanics: use virtual inheritance for a component

Namely, make BarycentricMapping inherit virtually from BaseObject, to
solve ambiguity issues in some other code that uses multiple
inheritance.


Former-commit-id: ada8f581dce215d63c0502444f8c5af6017f600a
FabienPean/sofa,Anatoscope/sofa,Anatoscope/sofa,FabienPean/sofa,hdeling/sofa,hdeling/sofa,FabienPean/sofa,FabienPean/sofa,FabienPean/sofa,FabienPean/sofa,Anatoscope/sofa,hdeling/sofa,FabienPean/sofa,hdeling/sofa,Anatoscope/sofa,hdeling/sofa,hdeling/sofa,Anatoscope/sofa,Anatoscope/sofa,FabienPean/sofa,FabienPean/sofa,hdeling/sofa,hdeling/sofa,Anatoscope/sofa,hdeling/sofa,FabienPean/sofa,Anatoscope/sofa,hdeling/sofa,Anatoscope/sofa