Expired Google credentials sometimes don't auto-update

[jpolitz]

When we get a 401 response from GDrive, we should be re-authenticating silently in the background. If this fails, we need to alert the user somehow, because it causes weird behavior in saving (messages like "program saved as undefined", which isn't true).

Need to check:

1. If reauth() is actually just not working, and fixing that function would help
2. How we can gracefully handle failure, and if we'll need to get the user to click something so we can reopen a popup to authenticate

This is a little hard to test on expiration, because it takes an hour for credentials to expire!

We probably want an option to save the program to localStorage so a user can refresh without losing valuable state.

[schanzer]

@jpolitz Is this still an issue?

[schanzer]

@jpolitz OK to close?