Make track changes sidebar an experimental feature as its incomplete

Change-Id: If373aa7a7efb338fd7a5305acbd19e95344a4bfc
Reviewed-on: https://gerrit.libreoffice.org/15995Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

officecfg/registry/data/org/openoffice/Office/UI/Sidebar.xcu

@@ -203,6 +203,9 @@
         <prop oor:name="OrderIndex" oor:type="xs:int">
           <value>600</value>
         </prop>
+        <prop oor:name="IsExperimental" oor:type="xs:boolean">
+          <value>true</value>
+        </prop>
       </node>
 
       <node oor:name="DesignDeck" oor:op="replace">