[WIP] update examples: 

In this PR: Nicer plots and titles in latent node example

Please review, as I'm not really sure what goes on in this example.

1) Are the titles appropriate?
2) It's not clear what the first row and second row mean, in the hidden variable plots. I think most ambiguity comes from the hidden patch grid and the visible grid having proportional shapes.  Would it work to have the visible image shape (6, 4) instead of (4, 4) and keeping the hidden one (2, 2) with the appropriate edges?