Implement initial shopping cart system

[amenconi]

Should be ready for functionality testing.

Left to do: Review responsive design for small viewports and modify UI accordingly.

[amenconi]

Initial shopping cart main feature set:

• Shopping cart icon in header that will open the cart in a modal.
• Shopping cart icon on NFT page and NFT cards on collection/nfts page with logic implemented to only display the icon for adding NFTs to cart if it passes same checks that allow the buy button to be visible on the NFT page.
• Notifications for when NFTs are added to cart, removed from cart or is blocked due to NFT already being present in the cart.
• Shopping cart to have the follow info per NFT added to cart: Image, Collection Name (linkable to collection page), NFT Name (linkable to NFT page), Royalties %, available for sale status, quantity / quantity available to add, [price] [token] per NFT and a remove icon. When cart loads, it will grab fresh Collection/NFT to display most up to date information and track if availability for sale of each cart NFT has changed or not.
• For NFTs that have more than 1 available for purchase (SFTs and Generated+Unowned etc.) have an input where quantity can be typed in or increased/decremented via up/down arrows.
• Checkout button that will launch an overlay with the cart checkout screen.
• Checkout screen will group each NFT from cart by network/token symbol since bulk order API requires a single network per call.
• NFTs in each group will display the following information: NFT Name (linkable to NFT page), Collection Name (linkable to Collection page), quantity, price per NFT, line item total showing price * quantity, a total row with sum of quantities and total price for all NFTs and quantities.
• If there are NFTs in cart that have become unavailable for sale, when checkout overlay loads it will warn the user that X number of NFTs were not included in the checkout review due to no longer being available for sale.
• Radio selector to choose which group of NFTs to purchase.
• Checkbox to agree to Terms and Conditions prior to Confirm and Lock button press which will generate the bulk buy transaction.
• Same process for purchase as single NFT buys with exception of button to "Show My NFT" upon purchase completion.
• "Sweep to Cart" button on collection/nft pages that will have a slider and a "Sweep to Cart" button. Upon slider select and button press, the collection NFTs available for sale will be sorted by price low to high and the top X NFTs added to the cart.