Previously actors that could be frozen under fog but were currently visible would be rendered by the frozen under fog system constantly in order to keep a copy of the renderables ready to go for the frozen counterpart when the actor became invisible. Instead, we now delay this extra rendering until the actor actually becomes invisible. This eliminates the wasted rendering to generate renderables that were never used.
The FrozenUnderFog.Tick method will now reuse the calculation do by the frozen actor when it had to calculate its visibility, this prevents it having to re-do the fairly expensive visibility calculation.
To resolve the ambiguity introduced when the introduction of isometric maps meant that cell and map coordinates were no longer equivalent, a new type has been introduced so they can each be represented separately.
