Simulate delay for cab signal upgrades

[YoRyan]

In the real world, cab signals occasionally display an unintended aspect for a brief few seconds. This phenomenon is called a "cab flip," and safety systems are programmed to handle it.

Due to the placement of track circuits and the performance of the onboard computer, there is also a perceptible delay between passing a wayside signal and the moment the train receives the corresponding cab signal.

It would be nice to simulate both of these effects.

[YoRyan]

Sources tell me that engineers don’t experience “cab flips” very often, so we’ll pass on those.

[YoRyan]

Implemented in 0bc82ebe0d1c35b676caaf00d52b3cb21dbd2d0a.