A sensor which registers mechs and trains attempting to pass by and, if necessary, blocks their movement.

If enabled, detects mechs/trains and blocks their movement if they are coming from any of the directions set by dir. Can currently only be enabled/disabled by radio command and airlocks are updated to utilize this.

The current setup allows mechs to move through airlocks during normal cycles, which for example lets Odysseus out to save lives.
Once a shuttle docks however, the sensors are enabled to prevent boarding.

If blocked, players receive a simple message stating that their command has been overridden.
Merge pull request #5791 from PsiOmegaDelta/Roadblock

Mech/Train sensor