This commit not only includes the bugfix for qt5 on ubuntu but also some improvments in the qt5 external project.

The fix concern only the following modification:

- add -qt-harfbuzz in the configure script to fix libz conflict

Other minor updates:

- upgrade qt version to last stable release 5.11.1
- remove commented cmake configuration related to qt4
- add options -optimize-size and -silent options in the configure script to optimize the package

see https://blog.qt.io/blog/2017/05/31/qt-lite-qt-5-9-lts/ for detail about the size optimization (contrl compiler flags)

silent option reduce the output generated in the build tree. Perhaps not a good idea...