Support SSL in the Graphryder server

[tanius]

Currently, one can only access the internal Graphryder API server with HTTP URLs. Due to this, a reverse proxy has to be added on top, for example with Apache2 or Nginx, in order to access the API in the Graphryder Dashboard, as long as the Graphryder Dashboard itself is served via HTTPS. Otherwise we'd get "mixed content" errors and the browser would refuse to talk to the Graphryder API.

To simplify this, Graphryder API should support HTTPS natively. And also obtain its own LetsEncrypt certificates for that.