Make separate "Deploy" action for Z-model engines

[jd284]

Currently the Z-model engines un-deploy when the engine is deactivated. I don't see a need for this, and it makes the space directly below the engine unusable or the animation would clip into it.
So it would be nice to have a separate "deploy" action for the animation, so that the engine can only be activated while deployed, but doesn't un-deploy on its own when the engine is deactivated.