MouseArea filling the image was eating mouse events which should be
handled by the list item. Handle them all at the list item level and
forward the "clicked" event to the extra content items which declare
the clicked() function.
https://doc.qt.io/archives/qt-5.6/qtquick-performance.html
In general, "property var" should be considered to be superior to "property variant" for every use-case from QtQuick 2.0 and newer (note that "property variant" is marked as obsolete), as it allows a true JavaScript reference to be stored (which can reduce the number of conversions required in certain expressions).
