qml: ReactionsPopup: Less visibility for icon

Too not be flashed by tons of smileys in the chat view (esp. noticable
in compact mode...)

Proper solution would be to only show the icon when hovering the line,
but that's a bit difficult with QML, see:

https://stackoverflow.com/questions/18135262/how-to-include-child-mouse-hover-events-in-the-parent-mousearea-using-qml