Adding Adagrad and Adadelta as ways of training the networks, and a demo that compares all the different approaches on MNIST dataset. This also required a new MultiGraph in build/vis, which I rather hastily and lazily added for now. Finally, NOTE: I changed the computation for momentum to a more standard formulation, so if you used SGD+Momentum previously in your networks, you may need to re-tweak it a little bit. In particular, you probably want to decrease it by up to factor of 10 or so.