MDL-32508 course/formats: Respect single page course display mode

Topics and weeks have been converted to use a shared renderer to output
their content.

Note, I started with good intentions but this renderer has mixed
paradgims due to fast and cheap winning out on the trinity.

AMOS BEGIN
   MOV [currenttopic,access],[currentsection,format_topics]
   MOV [currentweek,access],[currentsection,format_weeks]
AMOS END

course/format/topics/lang/en/format_topics.php

@@ -23,6 +23,7 @@
  * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 
+$string['currentsection'] = 'This topic';
 $string['sectionname'] = 'Topic';
 $string['pluginname'] = 'Topics format';
 $string['section0name'] = 'General';