Fix cap. issues with include files & QtCore include path

The capitalization is pretty self-explanatory. The QtCore change came about because that was the only file that required including the path /usr/include/qt5/QtCore - everything else was satisfied by the include directory /usr/include/qt5.

This still doesn't compile with PropWare's build system - I'm getting an error:
error: #error "Qt has not been ported to this OS - see http://www.qt-project.org/"
But that's probably because I'm including the wrong Qt stuff or defined my OS in the cmake toolchain file as Propeller.