Feature/categories filter contd

[brianfeister]

This is what we've been working toward for so long!!!

Querystring based UI state, the whole sidebar functionality works except initial page load, which I think I'll skip for now because of time

https://drive.google.com/file/d/1uaoZhetkpsJ0hVae7Qvvdd4nUILUtiw8/view?usp=drive_link