Add ability to install headers separately

:Release Notes:
Add cmake option 'SHIP_HEADERS_ONLY', to install only headers.
Add cmake option 'BUILD_WITHOUT_HEADERS', to build library
without installing headers.

:Detailed Notes:

:Testing Performed:
Unit-tests

:QA Notes:

:Issues Addressed:
[BHV-1839] [pmloglib] Deploy headers independently from the built targets

Open-webOS-DCO-1.0-Signed-off-by: Alexandr Smoktal <alexandr.smoktal@lge.com>

Change-Id: If3411cbbbc6aa78f184f5fc6787017fcb4631e59
Reviewed-on: https://g2g.palm.com/4912
Reviewed-by: DCO Verification
Reviewed-by: Alexandr Smoktal <alexandr.smoktal@lge.com>
Tested-by: Alexandr Smoktal <alexandr.smoktal@lge.com>
Reviewed-by: Anatolii Sakhnik <anatolii.sakhnik@lge.com>