bhyve graphics support

[Fabian Freyer]

Hi everybody,

I've added some code to support VNC Authentication (as much as a 16-byte
DES challenge response could be seen as Authentication) as per
https://tools.ietf.org/html/rfc6143#page-10.

It's my first time working with this reviews thing - I'm a bit unsure
how to set the diff to be based off the projects/ instead of head/, so
if I still need to change something, I would.

https://reviews.freebsd.org/D7029

It's been tested to work with TightVNC Viewer version 1.3.9. Not sure
about other ones - the RFC is a bit unclear here and there.

Fabian Freyer