Snowy Ice Room

Added falling snow to the Ice Room, with a new particle: ParticleSnow.
Falls at a slower rate (10% gravity) and has a random size (ranging from
1x1 to 3x3)

Added a new constructor and function for simply dropping PhysicsObjects
from a certain height above a certain position.

Fixed a PhysicsObject bug that would consistently cause PhysicsObjects
to fall short of their landing position.