Complete AI rewrite and other stuff

I've re written the AI as I thought of a better way to do things. The result is more realistic ants. I have also used a different technique to scale the ants. Ants can now be tiny - huge and everything in between but they don't look good too big so I'd still recommend keeping them to a realistic size, although if you want huge ants on your laptop etc, feel free ;)

Ant speeds scale much more with size now, so large ants are a lot faster than small ants.

I have also added an invisible tap to spawn button in the bottom left corner of the screen which makes spawning ants easier for mobile and tablet users without an A key.