Add a way to bulk request items for donation

[calexity]

As a Homeless Advocacy organization When I want to request a bunch of items I need Then I want to be able to do that using Spare.

Considerations

1. How to bulk add
2. How to select sizing for bulk add

[shawnadelic]

Technical description of what this would most likely look like:

• Use LocalStorage to store "cart" for items being donated/requested
• On "checkout", the app would read user's LocalStorage and build request form based on items in user's "cart"
• API endpoint would need to be updated to accommodate multiple items
• May need to update DonationRequest model to handle multiple items, maybe even add another model DonationRequestItem or something, with a ForeignKey pointing from DonationRequestItem to DonationRequest