I'm working to remove the usage of electron remote, and Auth windows are the last one. They open the auth in a new window. Since Github has started enforcing 2FA for almost everyone, the electron-window auth approach isn't functional for most. It therefore doesn't make sense to spend work maintaining the existing broken auth; instead, we can switch to a new one.

This change moves auth to open in the default browser. When Auth is done, it will redirect to gitify://oauth-callback, which the app will register and monitor, finishing the auth process when it's done.

At this point, I've got an initial approach started, but there's still lots to do. Help is welcomed.

There are several pieces left:

• Fix the start of the auth process
  • Allow the gitify://oauth-callback redirect in the Github app settings -- do we have access to that?
  • Fix the initialization of it -- all the types etc are broken, and the browser probably doesn't even open
• Catch and handle the completion of the auth
  • Communicate the auth from the main process to the App context, which started the Auth
  • Error handling
• Testing
  • Figure out automated testing approach, if possible
  • Manually test
• Documentation
  • Per Which Authorization callback URL should be used when setting up a new OAuth app? #395, document the changed redirect URI

Fixes #561
Fixes #650
Fixes #429
Fixes #485
Closes #395