Add setShaderId() for Mesh and Node

Mesh

Mesh.h

class Mesh {
...
public:
    ...
    void setShaderId(GLuint sid);
    ...
};

Mesh.cpp

void Mesh::setShaderId(GLuint sid) {
    shaderId = sid;
}

Node

If you are using a scene graph, then you also need to add setShaderId() in class Node

Node.h

class Node {
...
public:
    ...
    void setShaderId(GLuint sid);
    ...
};

Node.cpp

void Node::setShaderId(GLuint sid) {
    for (auto & m : meshes) {
        m->setShaderId(sid);
    }

    for (auto & n : childNodes) {
        n->setShaderId(sid);
    }
}