create 'hello controller'

new file: app/assets/javascripts/hello.js.coffee, new file: app/assets/stylesheets/hello.css.scss, new file: app/controllers/hello_controller.rb, new file: app/helpers/hello_helper.rb, modified: config/routes.rb, new file: test/controllers/hello_controller_test.rb, new file: test/helpers/hello_helper_test.rb