Eliminate some unnecessary abstraction.
Use send file instead of send data to stop sending empty .zip files.
Fix a typo, confirmation on delete request now actually appears.
Move directory clearing action into the controller.  Forces the app to block until the file is actually gone.  On even modestly large files we were getting back stale versions of the cart otherwise.
Update carts to be placed in tmp/carts/ and bound to session id rathern than the current user's NUID, which disallows unauthenticated use of the shopping cart.
Add a simple rake task for cleaning out shopping carts.  We'll want to daemonize this at some point.
Merge branch 'feature/shopping_carts_two' of https://github.com/nu-lts/drs into feature/shopping_carts_two

Mergin