Add mod_admin_extra as a commented module

Previous commits were done with:
for i in `git log --reverse --date-order --format=%h mod_admin_extra.erl`; do git format-patch -1 $i; cat 00* >>patch; rm 00*; done
Then editing patch to remove unneeded files and fix path.

ejabberd.yml.example

@@ -553,6 +553,7 @@ language: "en"
 ##
 modules: 
   mod_adhoc: {}
+  ## mod_admin_extra: {}
   mod_announce: # recommends mod_adhoc
     access: announce
   mod_blocking: {} # requires mod_privacy