CChaiGraphics::addMeshToRender() should specify parent mesh

[Michelle Yu]

So we can create compound mesh structures..

Change: CChaiGraphics::addMeshToRender(const std::string& arg_mesh_name, const std::string& arg_mesh_file, const Eigen::Vector3d& arg_pos, const Eigen::Matrix3d& arg_rot)

To: CChaiGraphics::addMeshToRender(const std::string& arg_mesh_name, const std::string& arg_mesh_file, const Eigen::Vector3d& arg_pos, const Eigen::Matrix3d& arg_rot, /*Optional / std::string arg_parent_mesh)

[Samir Menon]

Such a function already exists: CChaiGraphics::addMeshToParentInRender()