Add some maintenance instrustions to README.
Add country-wide aggregation for 2009 elections.
Add country-wide aggregation for 2004 & 1999.
Bugfix: don't display empty ward_pk attributes for voting district results.
Merge branch 'flask'

Conflicts:
	README.md
Serializers: only include results that are relevant to the specified event_type (national or provincial).
Serializer: Display national aggergate result as an attribute, not a list.