Add Peer to peer dbus support

[alexlarsson]

This adds a Server object that can be used to handle dbus clients connecting. It also adds server side authentication code, both the generic code and an EXTERNAL implementation.

There is a simple client/serve rdemo to test this, plus i verified connecting to the server with the gdbus implementation (from glib).

[guelfey]

Thanks for your contribution. I'll look at this as soon as I have time for it.

[philips]

this is great. Looking forward to seeing it merged.

[crosbymichael]

Any update on this PR?