Scheme API consolidation, OpenID improvements, client token file storage, test coverage.

Consolidate scheme API around authenticating an HTTP request. Distinct interfaces for dealing with token authentication (RFC 2617, pseudo-authentication OAuth) vs. "handshake" authentication (OpenID).

Using gorilla sessions and securecookies for the usso OpenID provider.

Introduced a file-directory structure for storing command-line client tokens.

Lots of test coverage added.