added blog functionality

[Pivotal tracker blog feature] (https://www.pivotaltracker.com/story/show/68944882)
1. Created posts & comments functionality
*Post has author, title, content & date
*Comment has name, date & body. References a post_id
2. Admin only can create & update posts. No deletion. Any user can create a comment but not delete.
3. Basic HTTP authentication required to create a new blog post with 
username = admin 
password = secret
4. Added blog link to footer
5. Created unit tests for Rspec models folder files & Acceptance tests for features folder files
6. Added Capybara gem
7. Four tests pending (Require Factory Girl)