Fix for duplicate (& orphan) devices

Fix for issue #14

Thanks @IngmarStein for reporting this - learned something new about HA today ;-)

Cause of recent changes in the identifiers object (of the DeviceEntry) (multiple) orphan devices might have been created - these orphan entries will be removed automatically with this release (cleanup could take a couple of seconds after the HA restart)

BREAKING CHANGE! (but only for users of multiple go-eChargers)

The DeviceRegistry Identifier has been changed (again) - this will create a new DeviceRegistry Entry per configured Charger - So IF you have multiple go-eChargers in your HA installation - you must adjust your automations (again) - since the deviceid's going to change - I am sorry for this inconvenience.