注册界面，自动根据浏览器语言，设置注册用户的语言

[baozhoutao]

https://github.com/steedos/steedos-accounts/issues/87

[baozhoutao]

https://github.com/steedos/steedos-accounts/commit/85e9c768785190eccd4316870ca4a9cb3df1b8fb

[baozhoutao]

数据修正脚本：

db.users.find({locale: {$exists: false}}).forEach(function(user){
    db.users.update({_id: user._id}, {$set: {locale: 'zh-cn'}});
    db.space_users.updateMany({user: user._id}, {$set: {locale: 'zh-cn'}})
});