added serializer and view for participating_orgs
added serializer and view for recipient countries
added id data to serializers and fixed error in recipient-countries url
added tests for recipient-countries and participating-organisations, and added some Factory classes to suply objects to these tests
Merge branch 'develop' of https://github.com/openaid-IATI/OIPA

Conflicts:
	OIPA/api/activity/serializers.py
Merge pull request #48 from Murrx/PR-rep-orgs_and_recip-countr

Added endpoints for participating organisations and recipient countries