Added support for ThrowablePotionItems, Crossbows

[JerryWester]

Crossbows need more work currently. Their power values are incorrect, and the line starts from the right side of the screen when the crossbow is in the center.

[zeroeightysix]

I couldn't reproduce crossbow arrows going further than the line says.

Aside from fireworks supposedly having gravity, this looks fine. We can't shift the line to the middle anyways, as you wouldn't be able to see its trajectory that way.