Added node modules to gitignore
Began cart construction

Added the basic boilerplate for shopping cart logic.

The "Shop" section now has a shopping cart in the top right, whose
quantity is derived from a cart that is stored in a user's browser.

The "Shop" section has a list of items derived from the JSON file in
`to-browserify/thingsForSale.json`, so items can be added freely.  Items
must all have a numeric ID, name, price, description, and image address.

The style of all the new additions can be edited in
`css/shopping-cart.css`.

The shopping cart items are currently being rendered very cheaply from
the html template file `to-browserify/menu-item.html`, and their
appearance can be changed there, as long as you do not change the
template tags in `{{doubleCurlies}}`.

Right now clicking the cart does nothing, and clicking items simply adds
them to the cart, and shows an alert with a rough approximation of what
has been stored in the cart.

No method to remove items from the cart has been added yet, nor has any
checkout implementation been added yet.

@fasdy