Add support for HTTP authentication

[lllama]

Our wiki uses HTTP Basic Authentication, so it would be useful if the Wiki constructor could take a HttpBasicAuthenticator, or a username/password pair, as an optional argument.

[lllama]

I've had a look at how to implement this myself, and it seems that I would have to pass in the HTTP Basic authenticator to the wiki class. This would then get passed on to the wiki info class, which the downloader class could then access when performing its REST API calls. The problem I'm having is modifying the signature of the wiki class's constructor. I'm guessing this is due to it being auto-generated somewhere.

[AndersHogqvist]

This would be a most appreciated feature!