[spike] Use signal-based triggers

[eirikbjornr]

📺 What

Inject a signal object to use event-based triggers.

🛠 How

Create a DebugController with a signal (EventTarget). Trigger events in BSP through the controller.

👀 See

Video of using the debug controller to trigger a failover and manifest reload: https://www.dropbox.com/s/plbpazq6tllt5gs/badger-spike-signal-triggers.mov?dl=0