3d model naming convention for parts with exposed pad

[poeschlr]

Right now we simply give the footprint and 3d model the same name (ignoring special suffixes)

This works quite well for most parts but kind of breaks down for parts with exposed pads especially if the pad is implemented as soldermask defined. (The footprint name parameters are specialized for footprint parameters that might not correlate to the package itself in such cases.)

One option would be to change this convention for at least EP packages such that the 3d model uses the nominal size of the slug on the package instead of the copper pad size.

This came up on the footprint generator: pointhi/kicad-footprint-generator#303