add special stylesheet for treewidget in the view properties toolbox
add special stylesheet for treewidget in the view properties toolbox

NicolasSchnitzler/medInria-public,aabadie/medInria-public,NicolasSchnitzler/medInria-public,NicolasSchnitzler/medInria-public,rdebroiz/medInria-public,aabadie/medInria-public,aabadie/medInria-public,rdebroiz/medInria-public,rdebroiz/medInria-public