Simplify display power behavior

This is supposed to avoid too much of a hassle when enabling brightnessctl in postmarketOS to save and restore display brightness over boots.

With these settings the display just switches off after 2 mins on battery or 5 mins with power plug connected. Further settings like reducing the backlight after a while, display blanking and display sleeping are disabled, as they may cause issues when handling the backlight. Users can nonetheless enable those features in the power settings if desired.

config/xfce4/xfconf/xfce-perchannel-xml/xfce4-power-manager.xml

@@ -4,5 +4,13 @@
   <property name="xfce4-power-manager" type="empty">
     <property name="show-tray-icon" type="bool" value="false"/>
     <property name="show-panel-label" type="int" value="1"/>
+    <property name="brightness-on-battery" type="uint" value="0"/>
+    <property name="brightness-on-ac" type="uint" value="0"/>
+    <property name="blank-on-battery" type="int" value="0"/>
+    <property name="blank-on-ac" type="int" value="0"/>
+    <property name="dpms-on-battery-sleep" type="uint" value="0"/>
+    <property name="dpms-on-ac-sleep" type="uint" value="0"/>
+    <property name="dpms-on-battery-off" type="uint" value="2"/>
+    <property name="dpms-on-ac-off" type="uint" value="5"/>
   </property>
 </channel>