KubeEdge Mappers-go v1.6.0 Release

New home for Device Mappers code

Device Mappers implementations now moved to its new home kubeedge/mappers-go from the KubeEdge main repo.

OPC-UA Device Mapper

OPC-UA Device Mapper with Golang implementation is provided, based on new Device Mapper Standard.
(mappers-go#4, @sailorvii).