Prefer named route helpers to raw strings

Declarations in config/routes.rb expose helpers methods accessible
in controller and view contexts. Using the named routes helpers is
less prone to error and makes refactoring routes easier.

Also, you can access these helpers through the `Rails` constant if you
want to play around with them in `rails console`:

```console
$ rails c
>> Rails.application.routes.url_helpers.tasks_path
=> "/tasks"
```


I :heart: pull requests!!!!