Install devise in test app

Here's a simple working install of Devise in the test Rails app in spec/rails_app.  It's about ready to install devise-capturable, but we can handle that on [install-devise-capturable-in-test-app](https://github.com/oreillymedia/devise-capturable/tree/install-devise-capturable-in-test-app).

It's largely based on [devise-test](https://github.com/oreillymedia/devise-test), but with a simplified controller (no books, no model, no views) that Devise is protecting with `authencate_user!`.