Re-implement S20Control power module

[TB-1993]

Goal: Re-implement the S20 power control module that was removed.

The S20Control powerModule was removed as part of #52. This needs reimplementing in an Apache compliant way. The easiest way to do this is to use the S20Control library provided here https://github.com/glenpp/OrviboS20/tree/master as a pip dependency and wrap it with our own implementation for the RAFT module.

Acceptance criteria:

• A power module for using the S20 power switch should exist
• The power module should pass powerswitch unit tests