add gnome-mpv and xfburn and fix indicies. (#30)

* fix path to gnome-mpv

* fix document viewer index

* start xfburn

* fix file name capitilization

* cleanup bad filename.

* add tweaking your desktop chapter blurb.

source/4/4.2/tweaking_your_desktop.rst

@@ -0,0 +1,10 @@
+Chapter 3.3: Accessories
+==============================
+
+This chapter contains the list of accessories installed by default.
+
+.. toctree::
+   :maxdepth: 2
+   :titlesonly:
+
+    4.2.1/openbox_configuration_manager