TMSS-190: as discussed with architect: no more need for subtask prio and schedule method.

SAS/TMSS/src/migrate_momdb_to_tmss.py

SAS/TMSS/src/tmss/tmssapp/migrations/0001_initial.py

SAS/TMSS/src/tmss/tmssapp/models/scheduling.py

SAS/TMSS/src/tmss/tmssapp/populate.py

SAS/TMSS/src/tmss/tmssapp/serializers/scheduling.py

SAS/TMSS/src/tmss/tmssapp/subtasks.py

SAS/TMSS/src/tmss/tmssapp/viewsets/scheduling.py

SAS/TMSS/src/tmss/urls.py

SAS/TMSS/test/testdata/subtasks.json

SAS/TMSS/test/tmss_test_data_django_models.py

SAS/TMSS/test/tmss_test_data_rest.py