Airborne assignment twak

[SiceX]

Airborne now cang be assigned only to species with the proper portrait. Specifically:

• all the avians
• the winged monkeys
• the dragon reptiles
• the big grasshoppers
• the big moths
• the balloon-like molluscoids
• the balloon-like fungi
• the balloon-like plantoids

I've also made it so that there's still a 5% chance of them not gaining the trait, because they can be like ostriches.

I also didn't touch fallen empires, because they can do what the heck they want.