BUG 1975 - yang unkeyed list is transformed to map node

Parsers and serializer for base, for concrete DOM type anf for composite
node structure to normalized node conversion were
added/modified to make it possible parse|serialize unkeyed list to|from
UnkeyedListNode and parse OrderedListNode.

yang-data-operations artifact - was added UnkeyedListNodeModification
class to handle cases when unkeyed list is loaded from input stream

Change-Id: Ia3a9554dea00bb9d424495a2b6ed1f96765be738
Signed-off-by: Jozef Gloncak <jgloncak@cisco.com>