Passing an empty path to the 3D model select dialog results in the file
select control displaying the root path which requires the user to drill
down to get to the 3D models. Use the KISYS3DMOD path as the default
and fall back to the project path as required for the initial file
select control path.
Clean up some coding policy violations.
Fixes lp:1737094
https://bugs.launchpad.net/kicad/+bug/1737094
4d64a2f53f