[Reviewer: Mike] Add command-line and user_settings options to disable authentication

Mike,

Please can you review this fix/enhancement to add command-line and user_settings options to disable authentication?  There are two parts to this.

*   The authentication module is only installed if the command-line option is set.
*   Bono now adds a plausible private ID (the default value) on the Authorization header if one hasn't been provided - previously, it reused the request URI, which is quite explicitly wrong as it contains the scheme.

This is not intended for deployment but can ease testing when working with an HSS for which there is no intersection of supported authentication types.

I've tested live, and enhanced the UTs to check this (previously they tested the wrong thing).

Thanks,

Matt