Add model.batch() method (+ minor fixes)

[#50612355]

e.g.:
model.batch(function() {
  // do something
});

instead of:
model.startBatch();
// do something
model.endBatch();
Implement .generateProtein() in genetic engine (move it from MD2D engine)

[#50612355]
Remove .generateProtein() from MD2D modeler and engine

[#50612355]