add answers model and linked it to questions

![687474703a2f2f6432327a6c627735666637796b352e636c6f756466726f6e742e6e65742f696d616765732f73746173682d312d353130333236653833393231642e676966](https://cloud.githubusercontent.com/assets/755201/5079406/1afea6d2-6e82-11e4-8adb-97972c30c984.gif)