Providing a Rails template

Can @jcoyne, @val99erie, @danhorst review this to see if I'm on the right path for a Rails template?

You can merge things if you want, but for now I'd like some :+1: or :-1: 

Once merged I'm going to update the README to indicate that you can do:

```sh
rails new curate_dce \
-m https://raw.github.com/ndlib/curate/planning-302/lib/generators/curate/application_template.rb
```

*Note: it would be master instead of planning-302