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`
I generally dislike this style (where the line break is between `expect` and `to).  I generally tend to use a local for the target:

``` ruby
contents = File.read( file('spec/rails_helper.rb') )
expect(contents).to match(/^require 'rspec\/rails'$/m)
```

...or put the line break at the opening paren on the matcher:

``` ruby
expect(File.read( file('spec/rails_helper.rb') )).to match(
  /^require 'rspec\/rails'$/m
)
```

That's just subjective personal preference, though.