Check pooled database connections before reusing them

Fixes #43

app.py

@@ -38,7 +38,7 @@ app.config["KI_LDAP_AUTH_PASSWORD"] = os.getenv("KI_LDAP_AUTH_PASSWORD")
 app.config["KI_LDAP_BASE_DN"] = os.getenv("KI_LDAP_BASE_DN")
 
 CORS(app)
-db = SQLAlchemy(app, session_options={"future": True})
+db = SQLAlchemy(app, session_options={"future": True}, engine_options={"pool_pre_ping": True})
 migrate = Migrate(app, db, compare_type=True)
 
 app.logger.info("Hello from KI")