Golang version of AuthN server enters Beta

The AuthN Server written in Go now meets and exceeds the feature set of the Rails version. Update docker images from keratin/authn to keratin/authn-server to make the switch. Testing has been performed to verify that the Go and Ruby versions are wire- and data- compatible, given the same configuration. If that proves to not be true, it is a fixable bug and may be backported to this v0.7 release branch.

New

• Error reporting harness, with initial integration for Sentry