Include pretender for non-production builds by default.

* Add pretender by default for non-production builds.
* Allow opting out with `includePretender: false`.
* Tests:
  * Add test to confirm a default install in development has `Pretender`
    available.
  * Add test to confirm that `Pretender` is **not** generated in
    production.
  * Add test to confirm that `includePretender: false` actually works.