Refine map styles

Swap dashed and solid border so Chicago has a dashed border and
Cook County has a solid border.

Use a different color pallete
(http://colorbrewer2.org/?type=sequential&scheme=OrRd&n=5)
for conviction rate choropleth instead of
grays to try to disambiguate with grays from base map.

Fixes https://github.com/sc3/cook-convictions/issues/142