consistent naming; moving functions from level.lua to gameworld.lua

data/scripts/entities/particle.lua

@@ -73,10 +73,5 @@ function Particle:HandleAnimation()
 end
 
 function Particle:DoPhysics()
-  if not self:isCollidingAt(self.pos.x + self.vel.x, self.pos.y, objects.collisions) then
-    self.pos.x = self.pos.x + self.vel.x
-  end
-  if not self:isCollidingAt(self.pos.x, self.pos.y + self.vel.y, objects.collisions) then
-    self.pos.y = self.pos.y + self.vel.y
-  end
+  self:Move()
 end