Session improve fix

This patch fix the session improve, which is based on [guanbo's commit](https://github.com/deployd/deployd/pull/184). I add a session config in user's config, and validate it when login.

I don't know how to handle the error while the type doesn't match. You can see how I do it in line 125 of user-collections.js, but I don't think it is right. I am looking for your advice, thanks.