Support persistent logins (OAuth refresh tokens)

[kepstin]

The current behaviour of MagicISRC requires that a user re-authenticate with MusicBrainz when their auth token has expired (or if the session storage in the browser is cleared). This is a few extra clicks in the workflow, so for people who use MagicISRC regularly it would be nice to have MagicISRC remember logins.

Some things to think about:

• Probably needs some login UI work so I can have a "remember me" option to enable persistent logins
• Store login information and refresh token in permanent storage rather than session storage
• When should the token be refreshed? Probably only makes sense to do this on ISRC submit (do I want to do it on initial page load?), but error handling and persisting data for re-login might be tricky.