add ID byte for A/D devices so we can identify them, and do unit conversion in the GW

[cbrake]

A/D convertor we are using: https://datasheets.maximintegrated.com/en/ds/DS2438.pdf

The A/D had 40 bytes of user memory -- propose we use two bytes of that to create a 16-bit ID.

Tasks:

• come up with a way to write ID into sensor nodes
• create documentation to list node types and IDs. To start, we have 10A current clamp, 20A current clamp, 50A current clamp.
• covert voltage data to correct units in GW and report back to portal as current, not voltage.