set config.secret_key_base, the Rails 4 config key for encrypting cookies
Remove all ActiveRecord mass-assignment settings from configs.

See http://guides.rubyonrails.org/security.html#mass-assignment if
you need help understanding Rails 4 mass-assignment protection
Remove ActiveRecord auto explain feature settings from configs
Merge pull request #47 from Devbootcamp/fix-rails4-deps

Fix Rails deprecation warnings