- Added capybara and several tests

- Added capybara 2.2.1 to the Gemfile
- Added FactoryGirl factory objects which contain sample data
- Added a helper method, sign_in_user, which signs in a user. This is
necessary for blog posts, as you have to be logged in to create or edit
a blog post
- Added tests to the blog controller, including two that test the
creation and edit of blog posts