Basic boss

Since I've changed the player to behave like a physics object, I want to get those changes merged back into master so they can be reflected on new code changes. Otherwise the work on the basic spider tank isn't done yet.
I converted this to a `List` so that the player could add `"Enemy"` to the weapons targets when they initialize their weapons, that way the weapon prefabs don't need to have `"Enemy"` as the default target.