Remove LiipThemeBundle

As baggy theme was removed and material is the only remaining theme, we don't need a theme switched anymore.
So:
- move all `*.twig` files from the material theme folder to the root
- remove useless translations

tests/Wallabag/CoreBundle/Controller/EntryControllerTest.php

@@ -86,7 +86,6 @@ class EntryControllerTest extends WallabagCoreTestCase
     public function testGetNew()
     {
         $this->logInAs('admin');
-        $this->useTheme('material');
         $client = $this->getClient();
 
         $crawler = $client->request('GET', '/new');