Merge pull request #248 from cnodejs/oauth

GitHub Oauth
Add allow-sign-up option

If not allow sign up, then nodeclub would close
local registry. And redirect /signup to login
with GitHub OAuth

[default] allow-sign-up: true
修复 loginname 的大小写问题
Merge pull request #252 from cnodejs/fix-login-name

修复 loginname 的大小写问题
Merge pull request #251 from cnodejs/allow-sign-up

Add allow-sign-up option
Fixed #253
Merge pull request #255 from cnodejs/session

Fixed #253
Update `xss` dependency
Merge pull request #257 from cnodejs/xss

Update `xss` dependency
写了 OAuth 部分的测试并小重构了一下

重构：
1. 重构 app.js 里面混乱的 app.use
2. 将 midderwares 纠正成了 middlewares