Replace DatasourceInterface with Selectable

library/Icinga/Data/DatasourceInterface.php

@@ -1,14 +0,0 @@
-<?php
-
-// TODO: create interface instead of abstract class
-namespace Icinga\Data;
-
-interface DatasourceInterface
-{
-    /**
-     * Instantiate a Query object
-     *
-     * @return BaseQuery
-     */
-    public function select();
-}

library/Icinga/Data/Selectable.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace Icinga\Data;
+
+/**
+ * Interface for classes providing a data source to fetch data from
+ */
+interface Selectable
+{
+    /**
+     * Provide a data source to fetch data from
+     *
+     * @return Queryable
+     */
+    public function select();
+}