Devise

PT Stories: 
- https://www.pivotaltracker.com/story/show/63805540
- https://www.pivotaltracker.com/story/show/63880110

- created model spec for users and view specs for sign in and sign up. 
- modified ```application_helper.rb``` with resource for devise
- updated factory for users.

#### Will wait with pulling this in until next scrum when we can do a code overview.

(Commits from Jan 14 & Jan 16 have already been merged with develop at a previous stage. )