Move subtask forecast to a plugin

Plugin repo: https://github.com/kanboard/plugin-subtask-forecast

app/Template/config/sidebar.php

@@ -34,7 +34,7 @@
         <li>
             <?= $this->url->link(t('Documentation'), 'doc', 'show') ?>
         </li>
-        <?= $this->hook->render('config:sidebar') ?>
+        <?= $this->hook->render('template:config:sidebar') ?>
     </ul>
     <div class="sidebar-collapse"><a href="#" title="<?= t('Hide sidebar') ?>"><i class="fa fa-chevron-left"></i></a></div>
     <div class="sidebar-expand" style="display: none"><a href="#" title="<?= t('Expand sidebar') ?>"><i class="fa fa-chevron-right"></i></a></div>