Grid: Custom cell properties now include a z configuration.
Grid: Custom cell properties now include a z configuration.

Also added a bit more documentation so it's easier to untangle
next time.

OpenTrons/opentrons-api,OpenTrons/opentrons-api,OpenTrons/opentrons-api,OpenTrons/opentrons_sdk,Opentrons/labware,OpenTrons/opentrons-api,OpenTrons/opentrons-api