Add project setup some models and a test

src/allmende_payment_system/database.py

@@ -0,0 +1,6 @@
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+
+SQLALCHEMY_DATABASE_URL = "sqlite:///./aps_db.db"
+engine = create_engine(SQLALCHEMY_DATABASE_URL)
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)