v0.0.0.108 - Airlock addition

Airlock doors have been added. If a room has 2 placed in its walls (one external, one internal),  they link and turn the room into an airlock (you'll notice the floor tiles update for that room).

 Only one airlock door will open at a time (if there is oxygen), and oxygen is stored (temporarily) before the external airlock door (rather than released to the outside).

No doubt some balancing and more visual clues will be required. But thought i'd get a release out as i've been working on this part for a bit now (and been distracted by other projects). There could well be issues if you add more airlocks than 2 to a room, or add normal doors. Will be putting in more checks and warnings for that. But hopefully if you do that airlocks will just behave like normal doors!

Nick