Please review #4400, "Avoid app_const when drawing routes in app generator"

The jist: by avoiding "MyApp::Application" in config/routes.rb
generator template, those generated config/routes.rb work out-of-box
when turning the app into an engine.

https://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/4400-patch-avoid-app_const-when-drawing-routes-in-app-generator

Thanks!
  --phil--