Add compatibility with 2.6 version of pbnjson

:Release Notes:
add back compatibility

:Detailed Notes:
add deleted virtual methods, mark them deprecated
fix tests

:Testing Performed:
Unit tests, build starfish

:QA Notes:

:Issues Addressed:
[BHV-2621] Develop a command line tool to validate JSON against schema

Open-webOS-DCO-1.0-Signed-off-by: Andrii Zora <andrii.zora@lge.com>

Change-Id: Ib066f36d69db093bfc32f082cd6c72d133868941
Reviewed-on: https://g2g.palm.com/5614
Reviewed-by: DCO Verification
Reviewed-by: Andrii Zora <andrii.zora@lge.com>
Tested-by: Andrii Zora <andrii.zora@lge.com>
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>