Add support for optional second clamps

[kevin1]

Added to product with launch of Flex Sensors and DCM in October of 2020.

What's new in: V33 (iOS/Android) V12 (Web): Dedicated Circuit Monitoring

@ritchierich For balanced 240VAC loads (no return path on a neutral) only one clamp is needed as the current path is a closed loop between the two split phase 240VAC wires. But you are correct both wires should not go through the clamp. He is not going to read any current with that setup.