leafletwidget application for specifying AMR regions in GeoClaw

GeoClawRegionRectangles.ipynb  can be used to select rectangles from a map and print out regions in the form needed in `setrun.py`.

Notebook can't really be viewed with nbviewer since the maps won't show up, missing the whole point, so I'm attaching a screen shot.

@cekees: I kludged something up so that it's possible to use a notebook with several maps at different resolutions and go back up and update an earlier one.  The problem is that `regions` is a global variable so it has to be set properly if you want to update an earlier map.  Maybe there's a better way to do this...
![regionrectangles](https://cloud.githubusercontent.com/assets/720122/5329702/50b1939e-7d72-11e4-80aa-6123c400cad4.png)