Devise setup done

@carolineartz @gpuglia  @mhamel01 I pulled from the development branch, then added/configured the Devise gem. Users can sign in/sign up now.

![screen shot 2014-06-06 at 9 29 09 pm](https://cloud.githubusercontent.com/assets/632721/3207548/92c7bcb6-edeb-11e3-8423-8899b71364a8.png)

## New Devise helpers
Devise added the following helpers:
1. `current_user`: This helper will be very useful to get the data model of a currently logged-in user. With this method, you are able to retrieve data stored in the database anytime you want it. For example, if I want to get the e-mail of the current logged-in user, I can retrieve it by calling the method `current_user.email`.
2. `user_signed_in?`: This helper returns a Boolean data type, which determines whether a user is logged-in or not. 
3. `user_session`: This is a session variable that can set anything you want in a hash format. Actually, this helper contains the subset of the Ruby on Rails session data. So, the purpose of this helper is to simplify the use of Rails sessions. Despite using the session variable for every Devise model that you have, you can utilize the session helper, so the session grouping for your model will be clear. For example, I want to save a string inside the session helper, I can do it by writing this code: `user_session[:hello] = "world"`

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**My concern is that I see sqlite files under /db. Didn't Mike delete those yesterday?**