Web UI: enable VNC over websockets

[ylei-tsubame]

This issue likely involves multiple parts:

• [x] Build websockify for putting a proxy between QEMU and the browser; this is required to "translate" VNC from QEMU to websockets, which allows connections from the websocket client on the browser.
• [ ] Setup self-signed certificate for wss:// (secured).
• [x] Enable clients from outside the subnet (firewall) to use VNC; this likely involves Apache ws_tunnel. No longer relevant because Apache has been replaced with the nodejs server.
• [x] ~Create mechanism to auto-generate token/passphrase for connection (as a temporary solution).~ Unnecessary for now because there are already 2 layers of authentication: 1) log in to the web UI, and 2) log in to the server VM.

[digimer]

^_^

[ylei-tsubame]

Regarding the certificate task: a Let's Encrypt certificate does not support binding to a public IP address, only self-signed certificate can do this. Since certbot only works with Let's Encrypt certs, we something else to handle the auto-create and auto-renewal process of self-signed certs. However, using a self-signed certificate likely doesn't clear browsers' warnings (which is the main objective of this task). Postponing until other higher priorities are cleared.

[ylei-tsubame]

Notes on handling the security on communication with the web UI components:

• First time setup use http
• Ask user whether they want to use self-signed or they provide the CA
• Redirect any http traffic to https after the user sets up the way to secure their communication
• wss can probably make use of the same certificate as https