Spreadsheet authorization

This does a few things:

* Verify, on login, that a user has access to view the site through a Google Spreadsheet
* On creating a new account, use the name from a Google Spreadsheet
* Refactor tests to reflect all the above
* Improve error message when login fails
Oh, I definitely agree there! Post-pilot we might want to consider having an evergreen email address (administrator@addressiq.org or something) that can be updated to point to the correct person... emphasis on "might," though, as it's added maintenance burden.