Add convenience functor classes for specifying linear spring and dampers.
Add convenience functor classes for specifying linear spring and dampers.

These functions can be used by derived classes for suspension templates that use ChLinkSpringCB force elements.

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