Add table of contents to epub of docs

(cherry picked from commit e1a71ea7a16834b7402944e6907e2b2a60ed63ba)

conf.py

@@ -315,3 +315,6 @@ rst_epilog = """
     image_locale="-" if language == "en" else language,
     target_locale="" if language == "en" else "/" + language,
 )
+
+# Needed so the table of contents is created for EPUB
+epub_tocscope = 'includehidden'