Added gated-autoencoder and an example

Hi again (sorry for the delay) I corrected my previous pull-request, now the gated-autoencoder uses CompositeSpace with Conv2DSpace or VectorSpace with the VectorSpacesDataset. Let me know what you think. 
This fails whenever the test is run from outside of the directory. Import using `from pylearn2.scripts.tutorials.gae_demo.make_random_dataset import generate`