[WIP] Add an extension for OpenID-based authentication.

Review Request #5199 — Created Jan. 6, 2014 and updated — Latest diff uploaded




[WIP] Add an extension for OpenID-based authentication.

This introduces OpenID-based authentication to Review Board 2.0. It
extends the login page to provide options for logging in using common
services, such as GitHub or Google. It accepts any OpenID provider.

This is still a work-in-progress. It needs the in-development
Review Board 2.0 beta 2 changes, and doesn't yet provide anything for
the My Account page. There's still documentation missing, some debug
output, and more testing that needs to be done.

This is heavily based on the work done by Patrick Uiterwijk.

Tested logging in with different services.