Run cron jobs via URL

Kanboard supports running cron jobs via CLI. There are hosting services
that don't offer CLI access, but they do offer calling a URL
periodically. This feature is often used as a CLI cron job replacement.

This commit adds a CronjobController called by "/cronjob" URL that will
execute cron jobs as they were executed via CLI. The URL has public
access, but is protected using the webhook token. The "/cronjob" URL
should be called via HTTPS.

app/Controller/CronjobController.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace Kanboard\Controller;
+
+use Kanboard\Controller\BaseController;
+use Symfony\Component\Console\Input\ArrayInput;
+use Symfony\Component\Console\Output\NullOutput;
+
+/**
+ * Class CronjobController
+ *
+ * Runs cron jobs via URL
+ *
+ * @package Kanboard\Controller
+ */
+class CronjobController extends BaseController
+{
+    public function run()
+    {
+        $this->checkWebhookToken();
+
+        $input = new ArrayInput(array(
+           'command' => 'cronjob',
+        ));
+        $output = new NullOutput();
+
+        $this->cli->setAutoExit(false);
+        $this->cli->run($input, $output);
+
+        $this->response->html('Cronjob executed');
+    }
+}