Find a nice way to create fake devices with some logic

[DominicOram]

Using the ophyd simulated devices is nice but we want some basic logic in them e.g. if we arm the zebra then armed gets set. It would be useful if we could get a device with this logic when we do i03.zebra(fake_with_ophyd=True)

[stan-dot]

@callumforrester , @DiamondJoseph thoughts?

[stan-dot]

@iain-hall we talked about simulating devices recently, we might want to define our use case in more detail here