Optimize the way tag list is rendered

Instead of retrieve all informations about entries of a tag to just count them, we’ll count them before with a fastest query.

Also change the layout of the tag list in material design

src/Wallabag/ApiBundle/Controller/WallabagRestController.php

@@ -387,7 +387,7 @@ class WallabagRestController extends FOSRestController
 
         $tags = $this->getDoctrine()
             ->getRepository('WallabagCoreBundle:Tag')
-            ->findAllTagsWithEntries($this->getUser()->getId());
+            ->findAllTags($this->getUser()->getId());
 
         $json = $this->get('serializer')->serialize($tags, 'json');