3D Part Preview added to Parts Tracker

[Orion Pobursky]

Bug identified and fixed in latest push to master branch.

I made the mistake of using the same markers for line vertices and triangle vertices, resulting in triangle vertices being marked as already being in use when they were not. This sometimes resulted in fancy gradient colors, and sometimes complete failures of texture loading.

Thanks for the bus report. This error would otherwise have affected all multi-colored parts.

Update pulled to server. Everything appears to be fixed.