add zh-CN translations for locomotive-cms to support chinese

I add zh-CN translations for locomotive-cms to support chinese. So you can fix issue #672 with chinese translations.But there also have another problem, the tinycme editor didn't show when I edit a rich text field if I set account language to chinese. I think it was caused by the locomotive-tinycme-rails gem, because of it lacked of a chinese lang package. I want you include the chinese lang package in your locomotive-tinycms-rails gem.