Bug 484 - Anyxml in sal-rest-connector

- RestconfImpl: handled AnyXmlSchemaNode

- JsonMapper: handled AnyXmlSchemaNode

- CnSnToJsonBasicDataTypesTest: added test cases for anyxml.

This commit depends (therefore is commited as draft) on commits:
- Add Anyxml normalized node to yang-data-api -
https://git.opendaylight.org/gerrit/#/c/7771/1
- Implementation of Anyxml builder -
  https://git.opendaylight.org/gerrit/#/c/8061/

Change-Id: Ib3da88cc6af96d98d139f7c1bbc94408ef9e814d
Signed-off-by: tpantelis <tpanteli@brocade.com>
Signed-off-by: Jozef Gloncak <jgloncak@cisco.com>