Original icons and avatar frame experiment

Changed all tab icons to white color. Changed import QtQuick 2.3 to all
that had 2.2. Applied ColorOverlay to tabs and added styleData.selected
logic. ColorOverlay seems to leave a white fringe. Tried to implement
circular mask for avatar images, but Image.PreserveAspectCrop is
cropping the image a bit too small when the image is not square.
However, this might be ultimately solved best by a user defined crop
area!