Some kicad import/export fixes

Hey Andete, I did a bit of work getting the kicad_mod import working. After these commits, kicad_old.py and kicad.py import my test KiCad footprints such that they generate identical coffee files (besides the UUID and some irrelevant 0 vs -0.0 distinctions)

Did some fixes for rendering of blank labels, and the coffee code generation for duplicate named pads, because both of those issues impact some of the kicad footprints I have.

I also did a little fix to kicad_old.py since it wasn't correctly handling KiCad's distinction between reference/value/user labels (the first two of which I see you normally handle as labels with the contents set to "NAME" and "VALUE" respectively)