create new shader for nomads build mesh

currently nomads factories use boxes with a special orange shader to create the printing effect of nomads units. This needs to be made a lot better. The new shader should have a texture and be semi transparent as before but not with a flat colour, so it looks like a printing effect.

The issue identifies Nomads factories and their existing special orange shader, but names no file or test. Start by locating the current factory shader and its printing-effect entry point; done means the effect uses a texture, remains semi-transparent, and no longer appears as a flat colour.

Written by the indexing model from the issue text.