Provide JSON value type in C++ API

:Release Notes:
Provide getType() method for JSON value.

:Detailed Notes:
Add getType() method to JValue class.
Add new method to unit tests.

:Testing Performed:
Unit tests

:QA Notes:

:Issues Addressed:
[BHV-36] pbnjson: Provide JSON value type in C++ API

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

Change-Id: Ib326b95df46d75bcd3d9647dbb4a29d6cf1ab3cc
Reviewed-on: https://g2g.palm.com/5224
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>