Add ExternalTaskManager class

app/Core/ExternalTask/ExternalTaskProviderInterface.php

@@ -0,0 +1,50 @@
+<?php
+
+namespace Kanboard\Core\ExternalTask;
+
+/**
+ * Interface ExternalTaskProviderInterface
+ *
+ * @package Kanboard\Core\ExternalTask
+ * @author  Frederic Guillot
+ */
+interface ExternalTaskProviderInterface
+{
+    /**
+     * Get templates
+     *
+     * @return string
+     */
+    public function getCreationFormTemplate();
+    public function getModificationFormTemplate();
+    public function getTaskViewTemplate();
+
+    /**
+     * Get provider name (visible in the user interface)
+     *
+     * @access public
+     * @return string
+     */
+    public function getName();
+
+    /**
+     * Retrieve task from external system or cache
+     *
+     * @access public
+     * @throws \Kanboard\Core\ExternalTask\AccessForbiddenException
+     * @throws \Kanboard\Core\ExternalTask\NotFoundException
+     * @param  string $uri
+     * @return array       Dict that will populate the form
+     */
+    public function retrieve($uri);
+
+    /**
+     * Save the task to the external system and/or update the cache
+     *
+     * @access public
+     * @param  string  $uri
+     * @param  array   $data
+     * @return bool
+     */
+    public function persist($uri, array $data);
+}