Only show suburbs in Cook County

Only show the census places in Cook County and don't show
census places in other counties that are part of Chicago's
MSA.  Update the suburbs.json file with a version that
only contains Cook County places.  Add Cook County's border
to the border file and name it chicago_cook_borders.json.

Update the JavaScript map views to use variable/parameter
names like ``borderCollection`` instead of ``chicagoCollection``.
This is both more general and more descriptive as the
layer described by these variables is the border of Chicago
and Cook County rather than Chicago neighborhoods and wards.
It's also no longer just Chicago.

Addresses https://github.com/sc3/cook-convictions/issues/133
Better suburbs layer

Add a version of the suburbs layer that does a better job of
clipping suburbs to Cook County.

Addresses https://github.com/sc3/cook-convictions/issues/133
Better city and county borders

Update border GeoJSON file with a version that doesn't have any offshore
areas.

Rename variables from ``chicago`` to ``borders`` to better reflect the
way that this layer now contains boundaries for both Chicago and Cook
County.

Style Cook County's border so it looks different than Chicago's.

Addresses https://github.com/sc3/cook-convictions/issues/133
Remove non-cook suburbs from existing suburbs.json

In the interest of time, us QGIS, the Spatial Query plugin and
a little research to remove non-Cook suburbs from the existing
suburbs.json (generated from the Spatialite database) rather than
wait for new data from the PostGIS database.

Addresses https://github.com/sc3/cook-convictions/issues/133
Merge branch 'cook_suburbs_only'