Some fixes for tags: authorization, translation…

can_use now takes all the open_for into account

config/locales/new_ui.en.yml

@@ -69,7 +69,7 @@ en:
       remove_default: Are you sure you want to remove the default tags?
   update:
     error:
-      tag: Error when updating category
+      category: Error when updating category
       tag: Error when updating tag
   url_alt: Alternative text
   use_default: Use Default

config/locales/new_ui.zh_tw.yml

@@ -69,7 +69,7 @@ zh_tw:
       remove_default: 您確定要移除此預設標籤嗎？
   update:
     error:
-      tag: 更新類別時發生錯誤
+      category: 更新類別時發生錯誤
       tag: 更新標籤時發生錯誤
   url_alt: 註解
   use_default: Use Default