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
'administer' --> 'administrator', please and thanks!

(Otherwise: Ideally we'd give an email address or something clearer, but this is good enough for the MVP.)