Update old example mods to work with latest game version

[WalterLPearson]

Update "artificial-plant", "exterior-air-vent", and "greenhouse" to work properly with the game version 0.12.0

[Sarai91]

"exterior-air-vent" seems to mostly work with the current version, other than some graphical glitches and an annoyance that could be classed as a bug: when you initially place a vent it is open. This is the default for interior vents (and makes sense there). However, I would say this isn't expected behavior from the player's perspective.