Remove `ActiveRecord` based settings from generated `rails_helper`

Improve support for Rails apps which do not use `ActiveRecord`. This does not add settings in the generated `spec/rails_helper.rb` file which are specific to `ActiveRecord`. This allows new apps to run without modification, instead of raising errors.

**To Do**

- [x] Check for `ActiveRecord` in the `rails_helper.rb` template
- [x] Spec out changes to the template
- [x] Do not attempt to run migrations if the example app does not use `ActiveRecord`
- [x] Implement a 2nd set of smoke tests which do not use `ActiveRecord`
> it seems like a specific object that no-one would actually use (as opposed to default Activerecord model)

Yep, that's true. It's my simple stand-in instead of pulling in another database gem, such as Mongoid, DataMapper, ROM, etc. It also means I can leverage most of the existing Rails generators without customizing them all.



> Maybe something like `example_app_generator` is a better name for the directory?

Yeah, I think that fits well. Hopefully there isn't much to change to update things that reference it.