Added 3 more door panel variants

Increased mesh polygon count, might cause a slight bit more lag when inserting/duplicating parts, but at least they look a lot less triangley now.

Added separate floor panel sections, it's also still available as complete mesh, but now as 3 separate sections + 2 separate transmission tunnel pieces as well.

Changed default materials, door panels/misc panels are now car-paint-colored by default, whereas floor panels are unpainted metal. Of course these can still be changed manually as well.

Release