Add column "Customer Group" of the order's customer to the Admin > Sales > DPD Orders grid

Every Magento shop using the shipper DPD should have installed the free module "DPD Shipping" for obvious reasons.

Weirdly enough the admin area of DPD Shippings does not have a column "customer group" under the "Sales > DPD Orders" grid, which shows the latest orders which are being processed with the DPD shipper. This would be a handy feature for obvious reasons, like being able to filter the orders by Commercial users or Normal users. Maybe you want to check the total revenue of a particular Customer Group which would be great knowledge for marketing reasons.

This while some columns are being redundant and unnessary.

Luckely adding this column is quite easy and only requires you to unzip this Git project in your Magento installation.