Bug 509: Fixed small discrepancies in Binding Data Change Events.

Bug 509: Fixed small discrepancies in Binding Data Change Events.

DataNormalizer which was responsible to render representation
of Instance Identifier in original format was introducing
additional node, when translation happened from normalized
to legacy, which is only triggered by Data Change Events.

Implementation of responsible algorithm was changed to
use schema in order to derive legacy InstanceIdentifier.

Data Change Events

 - Translated Data Change events were deserialized from
   DOM format on each access to fields, which may introduced
   CPU time overhead.

   Immutability of backing Data Change Events allows to
   add lazy caching of translated TOs, since event and data
   contained in Event Object are immutable.

 - getUpdated*Data in original Binding APIs returned
   both created and modified, so backwards-compatible fix
   was introduced.

Change-Id: Idab3dffb8651d50cca79a22ddcd43af29561b80e
Signed-off-by: Tony Tkacik <ttkacik@cisco.com>
Signed-off-by: Robert Varga <rovarga@cisco.com>