Merge pull request #6191 from RosettaCommons/roccomoretti/interactive_stale_jwt
[Foldit] Better handling of login issues.
If you have a stale or otherwise corrupted jwt in your local directory, then the client behaves very oddly. Check for this situation on login in a way the user can fix (i.e. by re-entering their password.)
Also make the error message on login failures a little more user friendly.