Allow to associate tags to colors

The color is then used as background in the board, list and task details
views

app/Template/task/details.php

@@ -156,7 +156,7 @@
             <div class="task-tags">
                 <ul>
                     <?php foreach ($tags as $tag): ?>
-                        <li><?= $this->text->e($tag) ?></li>
+                        <li class="task-tag <?= $tag['color_id'] ? "color-{$tag['color_id']}" : '' ?>"><?= $this->text->e($tag['name']) ?></li>
                     <?php endforeach ?>
                 </ul>
             </div>