Add cucumber to project.

Added the first cucumber feature - account login. Still has a failing
scenario, because the app is legitimately broken.

: #cucumber #test
Add sign-out link.

: #ui
Add default route for angular.

: #angular
Replace devise redirects with angular redirects.

: #devise #angular
Partially re-add Devise redirects.

I had to re-add some of the Devise redirects, specifically around
destroying sessions. Made HTML a navigable format so redirects would
be enabled. Changed the FailureApp to do full-on redirects when a
log-in failed so that we would render the correct URL.

: #devise