Add secure WebSocket support and probably figure out some automated certificate approach

[Cervator]

See https://forum.terasology.org/threads/facadeserver-headless-server-with-web-interface.1906/#post-15852 for some context. Might just be some Jetty option? @gianluca-nitti might know more / could figure it out

Ultimately this should allow us to https all the things - communication between this facade, its front-end running on http://utility.terasology.org:8000, the identity service also on http://utility.terasology.org (the default http port), and the meta server on http://meta.terasology.org (for modules)

For certificates likely auto-generate a self-signed cert for this facade and make it easy for the user to replace it with a legit one, like we could do for the instance hosted on utility.terasology.org