Implement fallback on accounts and full hits list

1. search on email (hashed or non hashed based on the settings of the App
2. if no results take the custom field value (if specified in the settings) and hit user API 
3. if no results take the custom field value (if specified in the settings) and hit Account API

![demo](https://f.cloud.github.com/assets/172804/1305253/f063d00a-3192-11e3-9ce0-30f507de6e93.gif)

/cc @maximeprades @shaialon