Images in contact preview are not shown with webkitgtk3 2.4.x

We have to unescape the image uri when running with webkitgtk3 2.4.x
and not just in versions prior to 2.2.x
Bug 732892 - Scale-down contact images in message preview

Set the maximal width and height of the contact image to 96 px. Also do
the same in the contact preview in addressbook.