Add technical drawing to Item record

[Simon Martin]

Update the system to accept another image - the technical drawing. I will do this in such a way that any number of images can be linked to a work shop item / product. When this is in place we will review printing these images, but for now the goal is to keep the technical drawings linked to the products

[Simon Martin]

emailed with suggestion to use teh existing image mechanism, which isn't used much anyway.