Add file preview for Markdown and text files

app/Template/file_viewer/show.php

@@ -1,8 +1,14 @@
 <div class="page-header">
     <h2><?= $this->e($file['name']) ?></h2>
-    <div class="task-file-viewer">
-        <?php if ($file['is_image']): ?>
-            <img src="<?= $this->url->href('FileViewer', 'image', $params) ?>" alt="<?= $this->e($file['name']) ?>">
-        <?php endif ?>
-    </div>
+</div>
+<div class="file-viewer">
+    <?php if ($file['is_image']): ?>
+        <img src="<?= $this->url->href('FileViewer', 'image', $params) ?>" alt="<?= $this->e($file['name']) ?>">
+    <?php elseif ($type === 'markdown'): ?>
+        <article class="markdown">
+            <?= $this->text->markdown($content) ?>
+        </article>
+    <?php elseif ($type === 'text'): ?>
+        <pre><?= $content ?></pre>
+    <?php endif ?>
 </div>