[Carnivores] Generate alpha channel based on face flags

[Ithamar]

When importing Carnivores models, generate the alpha channel in the output textures based on the face flags (transparent/opacity) and UV coordinates.

This would make converting from 'classic' models to the mobile format for example, much easier.

[Ithamar]

This would also make it easier to export Carnivores models to other games, since most use actual alpha in the textures (or allow more easily to export to seperate "mask" images)

[Ithamar]

actually, this could be done in reverse too, e.g. generate transparent/opacity flags based on the alpha channel of textures used in e.g. vivisector and/or primal prey, or any game really.