Extend auth error management for better coverage.

The auth error management wasn't checking for any auth errors, i.e.
if the auth error failed due to an auth error. This commit covers
that case as well.
Fix expired token test.

The PodioError was testing for expired token state on wrong terms
as it didn't check for "invalid_grant" errors from the Podio API.
Refactor auth error flow.

The previous implementation called EITHER the auth error
callbacks OR the generic error callbacks, but never both. This
flow has now changed to call both on authentication error.

This change enables greater flexibility when it comes to
dealing with re-auth attempts and how failures of such
should propagate to the client.