Update Cmake script to fix Qt5 build issue

 - Commit 4df1644 switched from use of QApplication to QCoreApplication
    but didn't update the CMake file to ensure QtCore include directories
 - Also drop unneeded references to QtWidgets

Verified by building

Open-webOS-DCO-1.0-Signed-off-by: Florian Hanel <florian.hanel@lge.com>
Open-webOS-DCO-1.0-Signed-off-by: Roger Stringer <roger.stringer@lge.com>

Change-Id: I438ee6062438f3ce662f221b650482b7c5364e17
Reviewed-on: https://g2g.palm.com/2819
Reviewed-by: Build Verification
Tested-by: Roger Stringer <roger.stringer@lge.com>
Reviewed-by: Eric Blade <eric.blade@lge.com>
Reviewed-by: Roger Stringer <roger.stringer@lge.com>