add devise authentication
- email/pass authentication
- "forgot my password" feature

- https://www.pivotaltracker.com/story/show/67751318
[Finished #67751318]
Updates based on PR comments

- #3
- https://www.pivotaltracker.com/story/show/67751318
[Fixes #67751318]
Merge pull request #6 from joshclick/devise_authentication

Devise authentication