Frontend: Validate the product quantities when creating an order

[chrishappy]

Since product quantities are not updated in real-time, it's possible that the quantities are invalid (e.g. a different client checked out some of the same items recently).

Thus, before we submit an order, we should check that the quantities are still valid.

[chrishappy]

// TODO: Validate the order before submitting
// Create a new function in cartHelper
// 1. use the promise in usePreviousOrderQuantitiesUpdater(), then
// 2. loop over all the products in the cart and check that the quantity
//      that is not greater than the maximum
// 3. if it is, make the color red and disable the button