Upgrade Rails to 4.1.8 and more

Remove RailsApi gem
Use respond_with in some places
scope the routes with json as default format
Article.public is now Article.published [*]

Be aware that previously, the token Devise used was publicly exposed: https://github.com/manshar/manshar/blob/master/backend/config/initializers/devise.rb#L7 Changing it might requires the users to change their passwords.