Prevent useless DB queries on plugin state checks

Author: cedric-anne

front/config.form.php

@@ -38,8 +38,7 @@
 
 } else {
 
-   $plugin = new Plugin();
-   if ($plugin->isInstalled("treeview") && $plugin->isActivated("treeview")) {
+   if (Plugin::isPluginActive("treeview")) {
 
       Html::header(PluginTreeviewConfig::getTypeName(),
                 $_SERVER['PHP_SELF'],