- Turn on foreign key constraint checking in the tests

- Change all ForeignKeyField's that refer to users to use our custom class, and mark those that allow robots
- Change robot delete to only execute the subset of queries necessary to actually delete robots

initdb.py

@@ -156,6 +156,9 @@ def setup_database_for_testing(testcase):
     initialize_database()
     populate_database()
 
+    # Enable foreign key constraints.
+    model.db.obj.execute_sql('PRAGMA foreign_keys = ON;')
+
     db_initialized_for_testing = True
 
   # Create a savepoint for the testcase.