Add ComputeNodalMass method to Tetra_4.
Add ComputeNodalMass method to Tetra_4.

This method allows to call the method "ComputeMassProperties" of ChMesh to find out mass properties of a FEA mesh. For now, it calculates the total mass.

dariomangoni/chrono,tjolsen/chrono,Milad-Rakhsha/chrono,amelmquist/chrono,armanpazouki/chrono,dariomangoni/chrono,andrewseidl/chrono,Milad-Rakhsha/chrono,projectchrono/chrono,armanpazouki/chrono,armanpazouki/chrono,amelmquist/chrono,andrewseidl/chrono,tjolsen/chrono,armanpazouki/chrono,andrewseidl/chrono,andrewseidl/chrono,rserban/chrono,tjolsen/chrono,jcmadsen/chrono,projectchrono/chrono,jcmadsen/chrono,dariomangoni/chrono,jcmadsen/chrono,Milad-Rakhsha/chrono,projectchrono/chrono,tjolsen/chrono,rserban/chrono,jcmadsen/chrono,amelmquist/chrono,rserban/chrono,jcmadsen/chrono,projectchrono/chrono,armanpazouki/chrono,rserban/chrono,Milad-Rakhsha/chrono,tjolsen/chrono,andrewseidl/chrono,Milad-Rakhsha/chrono,armanpazouki/chrono,amelmquist/chrono,dariomangoni/chrono,rserban/chrono,rserban/chrono,amelmquist/chrono,Milad-Rakhsha/chrono,jcmadsen/chrono,rserban/chrono,amelmquist/chrono,jcmadsen/chrono,dariomangoni/chrono,projectchrono/chrono,projectchrono/chrono,dariomangoni/chrono