Persons & Families (write) mutations in backend

Extend GraphQL API for Persons and Families to enable write operations.

This includes "attach/detach insuree to/from family", "move insuree from one family to another" and "make head of family" mutations.

WARNING:
Today there is a double FK between Insurees & Families.
According to discussion on https://openimis.atlassian.net/wiki/spaces/OP/pages/1366228996/Persons+Families+module+scope,
the FK from Insuree to Family must be made optional (via django migration)

This actually means that the mutation to create a new Family must include (and start by fetching/creating the head insuree