New feature suggestion: Add new overlay button

[fatman_n]

From "stable release", to "thermal upgrade" it was made some changes on "Oxygen Overlay" button, but I do not feel necessarily it was for the better. In "Stable" the different gases appears hovering in the room, very easy to see where the "Air Deodorizer" were going up, and where the "Air Scrubber" were going up, but even if showed oxygen in the room, the dupes could not breathe. Figured out from the plants that it was because of lack of atmospheric pressure. In "thermal upgrade" this is resolved because we now see where it is possible to breathe, and where it is not, but it made it difficult to see how gases sneaks away. So I suggest one "Gas Overlay" button that shows where the different gases are, and one "Atmospheric Preassure Overlay" button that shows where the pressure is high enough to breath, if there is breathable gases there.