Adds Users

Adds generic authentication model **Users** that will be the foundation for Coders, Organization Representatives, and Community members on CodeMontage. 

Authentication is based on the [**Devise**](https://github.com/plataformatec/devise) gem. Most of the default views have been imported [into the project](https://github.com/CodeMontageHQ/codemontage/tree/master/app/views/devise) for visibility and customization.

Key design decisions:
* Users do not have to confirm password on signup, can receive password reminders, can support confirmation (in case we have an issue with fake email addresses), and can login with a token (in case we want to log people in directly from emails)
* Email address and passwords are currently required for users
* [bcrypt encryption](http://bcrypt-ruby.rubyforge.org/) is used for all passwords