Fix exception_notification problem(forgot to update production.rb)
Add rails_12factor for heroku

Read more on https://devcenter.heroku.com/articles/rails-integration-gems
Remove config.assets.initialize_on_precompile
Change position gem 'rails_12factor', group: :production
Use assets_path in css
Bump twitter-bootstrap-rails to 2.2.7

To fix fontawesome issue
Generate ./bin directory that rails4 needs: `rake rails:update:bin`