fix(login): don't flash login screen at end of oauth flow

[jeffbcross]

After the oauth redirect flow, the user sees the login screen for a moment before being automatically redirected to the issues page.

The window location has a hash that indicates it's a redirect from the oauth flow. The app should look for this and prevent rendering anything until the auth state is updated.

Since the router strips the hash before rendering any component, we can't examine the hash from within a component. We'll probably need to get the hash before the application is bootstrapped to be able to examine it.

To reproduce:

• Visit the app https://issue-zero.firebaseapp.com
• Log in
• After successful login, watch the app load and notice the login screen flash.

[jeffbcross]

This has been fixed by 18552c1

TL;DR the redirect flow checks first if a hash matching the firebase redirect pattern is present, and if so, navigates to the issues page.