add test-outputdb.json
add fns and test coverage for atm purchases

Implements new controller functions and test coverage for handling
purchases for a specific atm transaction.  Specifically, adds API
for listing only one purchase, as well as deleting a purchase.

* add API for GET /api/atm/:atmId/purchase/:purchaseId
	-- this returns a single atm purchase, id'd by purchaseId

* add API for DELETE /api/atm/:atmId/purchase/:purchaseId
	-- this deletes a single atm purchase, id'd by purchaseId

* add test coverage to verify the above API calls (all tests passing)