Improve box detection where scanned poorly and allow for verification based on confidence

Improve box detection where scans are poor or where a pencil or other difficult to scan mark has been made by altering the box detection system. It currently works by using a threshold. This improvement should also help detection to work better over different scanner settings without making adjustments to thresholds. In addition, the box detection process should include a confidence interval in determining its selection. This will allow for manual verification to be limited to where boxes are difficult to detect.