Seismic volume example as IPython notebook.

This PR provides an IPython notebook to show the seismic volume example.

I made a few modifications to the example, to make what I thought was a nicer notebook example. In particular, this creates the volume directly and then processes it, and doesn't do anything with saving to any kind of file. I skipped the comparisons with NumPy, and only used a single filter example. I also added some plots of the per-trace statistics, to make that more interesting.

The PR as written depends on #476, which makes the commit list long, but it doesn't really depend much if at all on that. I have not tried to simplify that as I expect that PR to get merged first.