Desparate attempt to support retina on iOS/OSX

To make this application devicePixelRatio-resitant,
many hacks had to be added to the Image elements
in the Qml code.

TODO: As soon these bugs are fixed we can revert
the hack..

https://bugreports.qt-project.org/browse/QTBUG-38127
https://bugreports.qt-project.org/browse/QTBUG-38252