[displaymanager] make openbox session have "less priority".

Fixes settings Session= when both lxqt and openbox are installed, it will first find lxqt an use put lxqt.desktop
This fixes also #170

src/modules/displaymanager/main.py

@@ -35,10 +35,10 @@ desktop_environments = [
     DesktopEnvironment('/usr/bin/cinnamon-session', 'cinnamon-session'),
     DesktopEnvironment('/usr/bin/mate-session', 'mate'),
     DesktopEnvironment('/usr/bin/enlightenment_start', 'enlightenment'),
-    DesktopEnvironment('/usr/bin/openbox-session', 'openbox'),
     DesktopEnvironment('/usr/bin/lxsession', 'LXDE'),
     DesktopEnvironment('/usr/bin/startlxde', 'LXDE'),
-    DesktopEnvironment('/usr/bin/lxqt-session', 'lxqt')
+    DesktopEnvironment('/usr/bin/lxqt-session', 'lxqt'),
+    DesktopEnvironment('/usr/bin/openbox-session', 'openbox')
 ]
 
 def find_desktop_environment(root_mount_point):