Add ability to import/export tagging rules

- Add missing translations
- Add some tests
- Add `/api/taggingrule/export` API endpoint
- Add baggy theme
- Add error message when importing tagging rules failed
- Also fix all translations (I think we are good now)

tests/Wallabag/ApiBundle/Controller/TaggingRuleRestControllerTest.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace Tests\Wallabag\ApiBundle\Controller;
+
+use Tests\Wallabag\ApiBundle\WallabagApiTestCase;
+
+class TaggingRuleRestControllerTest extends WallabagApiTestCase
+{
+    public function testExportEntry()
+    {
+        $this->client->request('GET', '/api/taggingrule/export');
+        $this->assertSame(200, $this->client->getResponse()->getStatusCode());
+        $this->assertSame('application/json', $this->client->getResponse()->headers->get('Content-Type'));
+    }
+}