Monitoring document events with Python & Basic

-Mutual help pages x-refs
-tree addition
-new bookmarks for
--Advanced Basic Libraries
--Appl. Progr. Interface

NB: I wish I could create new </img> in gerrit

OH:
moved  new xhp to right position
New image
Update makefiles
several x-ref fixes

libO: Added language-driven <switch/> and <case/> tags for 3 different img captures
that XHP Editor doesn't propose but that are documented
Couldn't validate such switches.. crossing fingers..

OH: Languages are not switchable, as explained in comments.
Removed reference to image for good (not l10n full support).
fix missing apostrophe.

Change-Id: I97c92fc879df19f9e8de73e828cd3324ba2163fa
Reviewed-on: https://gerrit.libreoffice.org/70896
Tested-by: Jenkins
Reviewed-by: Olivier Hallot <olivier.hallot@libreoffice.org>

source/text/sbasic/python/python_examples.xhp

@@ -25,14 +25,15 @@
         </bookmark>
         <h1 id="hd_id201901031407"><variable id="pythonexamples2"><link href="text/sbasic/python/python_examples.xhp" name="python examples">Python programming examples</link></variable></h1>
     </section>
-    <!--
-    <embed href="text/sbasic/python/python_2_basic.xhp#python2basic"/>
+    <!-- WIP
+    <embed href="text/sbasic/python/python_dialog_handler#pythonhandler1"/>
     <embed href="text/sbasic/python/python_from_basic.xhp#pythonfrombasic"/>
     -->
     <embed href="text/sbasic/python/python_session.xhp#pythonsession"/>
     <embed href="text/sbasic/python/python_platform.xhp#pythonplatform"/>
     <embed href="text/sbasic/python/python_import.xhp#pythonimporth1"/>
     <embed href="text/sbasic/python/python_screen.xhp#ioscreen"/>
+    <embed href="text/sbasic/python/python_document_events.xhp#pythonmonitor"/>
     <embed href="text/sbasic/python/python_dialogs.xhp#pythondialog"/>
     <embed href="text/sbasic/python/python_listener.xhp#pythonlistener"/>
     <section id="relatedtopics">