Cutouts + curvature for quickflat

(1) Curvature underlays for quickflat.make_figure and quickflat.make_png
(2) Cutouts of particular regions of flatmaps implemented via another layer in the rois.svg file ("cutouts")

Should be up-to-date with master branch (rebased this morning). 

Still to do: 
implement curvature / cutouts for quickflat.make_svg
implement display of other svg file for labeling sulci / gyri / etc.