Make a notebook for opening subregions of images

[ctrueden]

And respond to this forum thread with a link.

[ctrueden]

This should be a new section in tutorial 2: opening images. The issue scifio/scifio#369 might pose a problem here. Ideally we want to give an example of opening very large data, but still only a subset, directly into a numpy array (wrapped to Java, of course). But SCIFIO doesn't support this, probably. So the next best thing would be a copy after opening a SCIFIO-backed disk-cached cell image.

[ctrueden]

It seems unlikely that scifio/scifio#369 will be fixed and merged, and a new SCIFIO released, and pom-scijava 32.0.0 released including it, new ImageJ2 and Fiji 2.4.0 releases built on it, within the next few days. So I'm bumping this issue. As soon as the SCIFIO bug-fix is easily available via PyImageJ, we can make this notebook!