Index drop places data - refs #31

* A drops can reference more than one place entity therefore
use the "location_rpt" fieldType as it allows for multi-valued
spatial data. This is only available in Solr 4.0+
Refactor DropIndexService#populatePlaces

* Renamed the method to getDropPlaces that now returns
a java.util.Map<Long, List<String>> that contains a string
representation of the coordinates for the places associated
with each drop