Add Dropdown to the Nav for the Marketplace page

[gabecorso]

Check out https://react-bootstrap.github.io/components/navbar/ for reference

We want to expand the NavBar to include a dropdown with links to new pages as shown in this screenshot

• [x] add a nav dropdown
• [x] add routes to the AppRouter for each of the new pages, Donate, Guild List, Your Bagdes, Free Market, Bounty Program, and Contact Us