Update Sponsor category when contract activated/terminated

- [NEW] Add 'Sponsor' category to partner upon contract creation
- [NEW] Replace 'Sponsor' by 'Old Sponsor' category
	upon contract termination if no other active contracts exist.
- [DEL] Remove tracking of 'sponsor_id' field in child_compassion as
	it is redundant with the 'state' field.
New Origin of contracts.

Added origin of contracts.