Bug 2374 - YANG Binding: Added support for AugmentationHolder interface

Bug 2374 - YANG Binding: Added support for AugmentationHolder interface

Binding specification v1 was originally designed and implemented
in only one implementation of interfaces in mind, which were generated one,
but during Helium additional implementation was introduced, but
specification and generated copy builder constructor did not accounted for
that change. Added additional interface which is implemented by LazyDataObject
that allow copy of augmenations.

Updated code generator to allow for that change and implementation of
LazyDataObject to support new interface contract.

Change-Id: I15aec38259f7f5e95301368d0264dfcf0571e2ba
Signed-off-by: Tony Tkacik <ttkacik@cisco.com>