Move respond_with to the responders gem

respond_with (and consequently the class-level respond_to)
are being removed from Rails. Instead of moving it to a 3rd
library, the functionality will be moved to responders gem
(at github.com/plataformatec/responders) which already provides
some responders extensions.
shouldn't be ?
```
redirect_to url_for(action: :show, id: project.id)
```