Handle Auth0 without redirect to make sign-up process smoother

[philippemnoel]

Feature Description
See below, this simply makes the auth process a big rough, although it's not a big deal

[rpadaki]

We should do the same as this: https://roberttolton.com/posts/implementing-auth0-authentication-into-a-chrome-extension.

Instead of launching auth from the WebUI, we should instead have the extension be the singular source of truth for auth, and communicate with the extension whenever it needs to deal with auth state.