Refresh access token on 401 response code

[Drumber]

Currently, the access token is only refreshed shortly before it expires. However, the access token may expire before the expected time (e.g. after changing the password). This causes all API requests to fail with a 401 response code, rendering the app unusable (unless you re-login).

To fix this, the access token should be updated when a 401 response code is received.