CART -- Minor bug-fixes and implementation details

[ianmichaeld]

• [ ] Currently, after logout the next visit to the cart page still shows the logged-out user's cart
• [ ] Make update occur on Enter as well as onClick
• [ ] Stylize subtotal
• [ ] Sometimes (first time?) updating quantity re-orders the contents of the cart
• [ ] When adding an item from all products, does not update the location tab in the navbar

[donleistman]

The navbar not updating issue is related to how Semantic-UI handles 'active' nav elements -- with state. Right now it's local state on the navbar component -- it would be nice to find a solution that maybe avoids adding the state to our Redux store. Or maybe that's the easiest way -- in any case, its low priority for now.

Best "solution" may be to NOT redirect to the cart after we add an item, but rather have a visual indicator that something was added from the Browse view -- such as a number updating on the cart button, and/or a popup box near the cart showing the item we added and letting us update quantity.