lookupapi: support users not of the form {scheme}:{identifier}

This change is currently deployed to the live service since otherwise the IAR is broken.

Lookupapi still had the implicit assumption that users would be named {scheme}:{identifier} when created by django-automationoauth. That is no-longer true and caused lookup proxy to fail when re-deployed.

With an abundance of caution, make sure we support all schemes we have used historically until we're sure nothing will break if we remove them.

Additionally, fix build errors on tox by making use of the psychopg2-binary package.