Add basic HTTP authentication to archive POST/DELETE.

The credentials can be stored in the charmd configuration file.
Abstract out the authentication logic in a decorator.
Created a card for the DoRequest refactoring.
Re HandlerConfig, I am not sure I understood what you are suggesting. Using two different structures for NewServer and the underlying real handlers? About the placement, while it's true that HandlerConfig is not an HTTP API endpoint parameters, it's also true that it's still an external API parameter, not just a function argument. But I am sure I am missing your real point here.