last remaining counter + gaps allowing

[benlp91]

The last two remaining tasks to make FX modding more user-friendly for a long time are: removing the count in terrain.cfg (room count and slab count) and allowing gaps in effects.toml. All values should be readable until 2000. -EDIT there's also a columnset.toml and slabset.toml that should have the same abilitys (count is already gone but it does not allow gaps)