Fix notification icon not appearing in Unity

Unity's indicator expects certain properties to be exported by an
application, of which Quassel is lacking some. This adds IconThemePath,
Menu, ItemIsMenu to org.kde.StatusNotifierItem.

Thanks a lot to shiznix for providing this patch.

Fixes #1269

interfaces/org.kde.StatusNotifierItem.xml

@@ -8,6 +8,10 @@
     <property name="Status" type="s" access="read"/>
     <property name="WindowId" type="i" access="read"/>
 
+    <!-- An additional path to add to the theme search path to find the icons specified above. -->
+    <property name="IconThemePath" type="s" access="read"/>
+    <property name="Menu" type="o" access="read"/>
+    <property name="ItemIsMenu" type="b" access="read"/>
 
     <!-- main icon -->
     <!-- names are preferred over pixmaps -->