[#15] Ensure that bounding boxes are defined counter-clockwise

To return correct results on a spatial query, rectangle geometries must
be defined in counter-clockwise order [1]. This changeset adds a small
sanity check to before_index when we are dealing with a Polygon geometry
that has 5 coordinate pairs. Shapely is used to generate a LinearRing
from the polygon coordinates and check if they are ccw. If not, they are
reordered and a new polygon is generated so the WKT sent to Solr is
properly ordered.

The GeoJSON template used for extents in the base spatial harvester has
been also updated to define the coordinates counter-clockwise.

[1]
http://wiki.apache.org/solr/SolrAdaptersForLuceneSpatial4#JTS_.2BAC8_WKT_.2BAC8_Polygon_notes