Make kill switch timing testable without sleeps

[holsee]

Refactor kill_switch function into own module to allow time-based unit testing without Proces.sleep call.

[holsee]

From the discussions which took place at the Tuesday 2nd July Meet-up:

• We need to refactor the kill switch mechanism into its own module
• We need a means by which this dependency can be passed into the Service process
• A test version of the kill-switch needs to be created that will allow for introspection of the timeout value passed into it, as well as a means to manually trigger the kill switch signal.