Add Themes: Dark, light and automatic mode

app/Model/ThemeModel.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace Kanboard\Model;
+
+use Kanboard\Core\Base;
+
+/**
+ * Class Theme
+ *
+ * @package Kanboard\Model
+ * @author  Frederic Guillot
+ */
+class ThemeModel extends Base
+{
+    /**
+     * Get available theme
+     *
+     * @access public
+     * @return array
+     */
+    public function getThemes()
+    {
+        return [
+            'light' => t('Light theme'),
+            'dark' => t('Dark theme'),
+            'auto' => t('Automatic theme - Sync with system'),
+        ];
+    }
+}