Issues/738 za constituency areas

Closes #738

Once merged the DA areas can be updated by:

- download [geocoded data](https://docs.google.com/spreadsheet/ccc?key=0Am9Hd8ELMkEsdHpOUjBvNVRzYlN4alRORklDajZwQlE#gid=0) as a CSV file
- run ` ./manage.py  south_africa_set_da_office_locations --commit downloaded_data.csv`