Re-add deprecated Pico::getBaseThemeUrl() to maintain BC

lib/Pico.php

@@ -2240,6 +2240,18 @@ class Pico
         return substr($path, $contentDirLength, -$contentExtLength) ?: null;
     }
 
+    /**
+     * Returns the URL of the themes folder of this Pico instance
+     *
+     * @deprecated 3.0.0
+     *
+     * @return string
+     */
+    public function getBaseThemeUrl()
+    {
+        return $this->getConfig('themes_url');
+    }
+
     /**
      * Returns the URL of a given absolute path within this Pico instance
      *