Many documentaries steeped in social or political issues get very insistent and often very noisy in expressing a point of view. Michael Moore is of course the model for effective, engaging and defiantly in-your-face activism in this arena.  In contrast, “The Ghosts in Our Machine,” a heartfelt meditation on animal rights, comes at you as a whisper. It depends on the persuasive powers of creatures great and small — in their natural habitat or in cages — to argue that we stop using them for food, clothing, research and entertainment. That the cages be tossed away.