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)

src/Wallabag/CoreBundle/Resources/translations/messages.en.yml

@@ -140,6 +140,15 @@ config:
         edit_rule_label: 'edit'
         rule_label: 'Rule'
         tags_label: 'Tags'
+        card:
+            new_tagging_rule: Create a tagging rule
+            import_tagging_rules: Import tagging rules
+            import_tagging_rules_detail: You have to select the JSON file you previously exported.
+            export_tagging_rules: Export tagging rules
+            export_tagging_rules_detail: This will download a JSON file that you can use to import tagging rules elsewhere or to backup them.
+        file_label: JSON file
+        import_submit: Import
+        export: Export
         faq:
             title: 'FAQ'
             tagging_rules_definition_title: 'What does « tagging rules » mean?'
@@ -603,6 +612,8 @@ flashes:
             entries_reset: Entries reset
             archived_reset: Archived entries deleted
             otp_enabled: Two-factor authentication enabled
+            tagging_rules_imported: Tagging rules imported
+            tagging_rules_not_imported: Error while importing tagging rules
     entry:
         notice:
             entry_already_saved: 'Entry already saved on %date%'