Added ProposalDuplicates model and logic. This will be used for storing the answer on duplicate calculations. Patch by: Lennard de Rijk Reviewed by: to-be-reviewed

# Geo-enabled Sitemap classes.
from django.contrib.gis.sitemaps.georss import GeoRSSSitemap
from django.contrib.gis.sitemaps.kml import KMLSitemap, KMZSitemap