introduce schema building by traversing jvalue

:Release Notes:
New API to parse schema from jvalue.

:Detailed Notes:
- tie together jtraverse and jschema_builder
- expose schema builder and parsing callbacks in public API
- add unit-tests for parsing schema from jvalue

:Testing Performed:
unit-tests

:QA Notes:

:Issues Addressed:
[BHV-3085] Provide pbnjson API for schema construction from jvalue

Open-webOS-DCO-1.0-Signed-off-by: Nikolay Orliuk <nikolay.orliuk@lge.com>

Change-Id: Ica96a9e7e6826487996e66e63785c49df2e6816c
Reviewed-on: https://g2g.palm.com/5145
Reviewed-by: DCO Verification
Reviewed-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Tested-by: Nikolay Orliuk <nikolay.orliuk@lge.com>
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>