Add joining of multiple accounts

I added the ability to join multiple accounts.
The saveOrUpdate function creates a new user or joins the new data to the existing user.
This Pull Request has been tested with all implemented providers (Facebook, Twitter, Google, Linkedin).
![2014-04-09 10 16 37 am](https://cloud.githubusercontent.com/assets/2142829/2653257/4df53aaa-bfbf-11e3-9335-e36fda93a8a2.png)