improve cameras

cleanify cameras inventory, allow for multiple cams per restaurant, cleanify rtsp capture, fix websockets in video-capture, allow detection of checkouts

backend/video_capture.py

@@ -75,4 +75,4 @@ async def handle_cameras():
                     db.add(db_record)
                     db.commit()
                     await manager.broadcast(json.dumps({"type": "data"}))
-        time.sleep(60 - (datetime.now() - current_date).total_seconds())
+        time.sleep(max(0, 60 - (datetime.now() - current_date).total_seconds()))