libxfce4ui: add glade package

* To edit glade files for xfce-packages it needs libxfce4ui's catalog [1].
* Unfortunately some host distributions do not supply a libxfce4ui-glade package.
* By installing glade3 + libxfce4ui-glade it is now possible to edit xfce's
  glade-files on target machine.

[1] http://comments.gmane.org/gmane.comp.desktop.xfce.devel.version4/20021



Signed-off-by: Andreas Müller <schnitzeltony@googlemail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>