Make font DPI changable for device package post-install scripts (MR 8)

Implementing the font DPI in the configs does not change anything
actually. However, having the value in the configs allows it to be
overwritten by device packages post-install scripts. That way devices
with high resolution screens can be assigned a larger text
representation on Xfce4 installation.

config/xfce4/xfconf/xfce-perchannel-xml/xsettings.xml

 <?xml version="1.0" encoding="UTF-8"?>
 
 <channel name="xsettings" version="1.0">
+  <property name="Xft" type="empty">
+    <property name="DPI" type="int" value="96"/>
+  </property>
   <property name="Gtk" type="empty">
     <property name="DecorationLayout" type="string" value="menu:minimize,maximize,close"/>
   </property>
   <property name="Net" type="empty">
     <property name="IconThemeName" type="string" value="Faenza-Ambiance"/>
   </property>
-</channel>
\ No newline at end of file
+</channel>