Login using Clever

At least one Louisiana middle school has asked for an alternative to Google for login, based on the fact that they can't get admin to sign up or Apps for Edu accounts. They suggested using clever.com. They said that clever.com accounts act a lot like Google accounts, and they are able to use Google Docs with them. That's surprising, but I don't know anything about it. In any case, I should look into what it would take to add support for clever.com. This might also relate to work that @rcook was doing.

The issue names no files, tests, or entry points; start by investigating how login currently works and reviewing the related work mentioned for @rcook. The scope and completion criteria for adding Clever support are not defined in the issue.

Written by the indexing model from the issue text.