Data/interfaces: add Filterable, extend Connection

New interface ConnectionInterface attempts to aggregate things.
Extended Filterable interface, added Filter-related functions. Please
note that apply will probably get dropped later on, I'll keep it for
compatibility reasons right now.

refs #6418

library/Icinga/Data/ConnectionInterface.php

@@ -0,0 +1,5 @@
+<?php
+
+namespace Icinga\Data;
+
+interface ConnectionInterface extends Selectable, Queryable {};

library/Icinga/Data/Filterable.php

@@ -2,7 +2,20 @@
 
 namespace Icinga\Data;
 
+use Icinga\Data\Filter\Filter;
+
 /**
  * Interface for filtering a result set
  */
-interface Filterable {}
+interface Filterable
+{
+    public function applyFilter(Filter $filter);
+
+    public function setFilter(Filter $filter);
+
+    public function getFilter(Filter $filter);
+
+    public function addFilter(Filter $filter);
+
+    public function where($condition, $value = null);
+}