Add Variables extension

Dockerfile

@@ -82,3 +82,8 @@ RUN git clone --depth 1 \
 RUN git clone --depth 1 -b $MEDIAWIKI_BRANCH \
     https://gerrit.wikimedia.org/r/mediawiki/extensions/CSS \
     /var/www/html/extensions/CSS
+
+# https://www.mediawiki.org/wiki/Extension:Variables
+RUN git clone --depth 1 -b $MEDIAWIKI_BRANCH \
+    https://gerrit.wikimedia.org/r/mediawiki/extensions/Variables \
+    /var/www/html/extensions/Variables

LocalSettings.php

@@ -226,6 +226,8 @@ $wgVirtualRestConfig['modules']['parsoid'] = array(
 
 wfLoadExtension( 'TemplateData' );
 
+wfLoadExtension( 'Variables' );
+
 wfLoadExtension( 'CSS' );
 
 require_once "$IP/extensions/Widgets/Widgets.php";