update Piwik to version 2.16 (fixes #91)

www/analytics/core/Plugin/AggregatedMetric.php

@@ -0,0 +1,21 @@
+<?php
+/**
+ * Piwik - free/libre analytics platform
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/gpl-3.0.html GPL v3 or later
+ */
+namespace Piwik\Plugin;
+
+
+/**
+ * Base type for metric metadata classes that describe aggregated metrics. These metrics are
+ * computed in the backend data store and are aggregated in PHP when Piwik archives period reports.
+ *
+ * Note: This class is a placeholder. It will be filled out at a later date. Right now, only
+ * processed metrics can be defined this way.
+ */
+abstract class AggregatedMetric extends Metric
+{
+    // stub, to be filled out later
+}