Collapsible Sidebar

[lowtorola]

Currently, our new frontend's sidebar is not collapsible! This is quite inconvenient, especially on mobile devices. We should have a hamburger menu that opens/closes the sidebar (ideally with an animation). Below are some target goals for this endeavor:

• Add hamburger menu to the top left of our header bar that opens/closes the sidebar (see lovely diagram)
• Stash sidebar state in cookies so that users can choose to leave the sidebar closed 🍪
• Add an animation to the sidebar transition (implementer's choice!)
• Always default the sidebar to closed on mobile 🥇

To get started, check out our sidebar's source code in index.tsx! Then, when you've gotten a handle on how you might go about opening/closing it (hint: check out the collapsed prop 😃) you can try to make it toggle-able! Note that our Header.tsx component already has a hamburger menu that can open/close its own menu for mobile, so maybe think (and ask!) about how you could integrate the header and sidebar to work together (consider using a Context).