Make UI publicly accessible for viewing

[Mr0grog]

I’m working on making public read access to the API a thing (edgi-govdata-archiving/web-monitoring-db#1069), and once that’s done, the UI needs to be able to take advantage of it by not requiring people to log in to view things. It should still be possible to optionally sign in, but not required.

There are some write-focused parts of the UI, and those still need to require login. At the moment, they are all turned off anyway. It might make sense to remove them entirely; otherwise we should add additional code gating their visibility on someone's logged-in status.