added PatientSerializer, AmbulanceCallTimeSerializer
modified CallSerializer for one-to-many relation
added test_calls.py for testPatientSerializer and testCallSerializer
You should also add a separate test for AmbulanceCallTimeSerializer. AmbulanceCallSerializer should also have a patient_set field, just like ambulancecalltime_set.
added PatientSerializer, AmbulanceCallTimeSerializer modified CallSerializer for one-to-many relation added test_calls.py for testPatientSerializer and testCallSerializer