improved invoices with new renderer (#306)

* added docx renderer and demo template
* added csv renderer and demo template
* added xlsx renderer and demo template
* added ods renderer and demo template
* added user calculator
* added invoice documentation

src/Invoice/RendererInterface.php

@@ -0,0 +1,34 @@
+<?php
+
+/*
+ * This file is part of the Kimai time-tracking app.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Invoice;
+
+use App\Entity\InvoiceDocument;
+use App\Model\InvoiceModel;
+use Symfony\Component\HttpFoundation\Response;
+
+interface RendererInterface
+{
+    /**
+     * Checks whether the given InvoiceDocument can be rendered.
+     *
+     * @param InvoiceDocument $document
+     * @return bool
+     */
+    public function supports(InvoiceDocument $document): bool;
+
+    /**
+     * Render the given InvoiceDocument with the data from the InvoiceModel.
+     *
+     * @param InvoiceDocument $document
+     * @param InvoiceModel $model
+     * @return Response
+     */
+    public function render(InvoiceDocument $document, InvoiceModel $model): Response;
+}