[#632] API filtering on name and iati_org_id for organisation

Add simple filtering of organisations on the name and iati_org_id fields.
This is used to find orgs in create_rsr_data.py
[#632] Enable the adding of Partnership objects

To be able to add Partnerships to Projects a way to do lookup of the
Organisation linked to in the Partnership is needed.

This solution does lookup via the API using the Organisation.iati_org_id
field primarily and if that does not exists lookup is done using
Organisation.name.

Add RSRModelInstance.partnership__organisation method.

Add more docstrings and comments.

Several small code fixes.
[#632] Add data to JSON files

Add partnership objects to project_1.json

Fixes to organisation data.