add current_cart method with pending specs
add before destroy hook to ensure no line items reference a product - pending specs
add to cart functionality
default line_item quantity to 1
spec line items controller
refactor and spec current cart
spec ensure_line_item_not_referenced_by_product
use find_by_id in current_cart.

Find throws an exception when no record is found. It is possible to have
a cart_id stored in the session but no carts in the database. This is an
edge case but using find_by_id returns nil, and doesn't throw an exception
specify rails-money gem version. It was looking for an old one and failing on bundle install, because why not...
add destroy action to cart
WIP add product
mark product create as pending cause I fail
Merge branch 'add-product'