This changeset integrates the AccessController into the main registry app. This
includes support for configuration and a test implementation, called "silly"
auth. Auth is only enabled if the configuration is present but takes measure to
ensure that configuration errors don't allow the appserver to start with open
access.
Most conditional parsing code has been moved into UnmarshalYAML
functions for simplicity
Uses the BrianBland fork of goyaml in configuration.go temporarily until
fix https://github.com/go-yaml/yaml/pull/52 is merged in