xfce-app.bbclass: just set SRC_URI commmon to most xfce-apps

* build tested with source download for xfce4-notifyd and xfce4-screenshooter
* run tested on overo

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

meta-xfce/classes/xfce-app.bbclass

@@ -0,0 +1,4 @@
+inherit xfce
+
+SRC_URI = "http://archive.xfce.org/src/apps/${BPN}/${@'${PV}'[0:3]}/${BPN}-${PV}.tar.bz2"
+