Implement interface "Browsable" for classes providing page turning

This interface is intended to be used everywhere a Zend_Paginator
is returned within our code.

library/Icinga/Data/Browsable.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace Icinga\Data;
+
+/**
+ * Interface for browsing data
+ */
+interface Browsable
+{
+    /**
+     * Paginate data
+     *
+     * @param   int $itemsPerPage   Number of items per page
+     * @param   int $pageNumber     Current page number
+     *
+     * @return  Zend_Paginator
+     */
+    public function paginate($itemsPerPage = null, $pageNumber = null);
+}