Do not allow mixed-content WebSockets

[xael-fry]

Pla should delivered wss on HTTPS pages.

When a attempts to open a WebSocket to a non-TLS-protected server ("ws://"), the attempt fail if the document was delivered over HTTPS.
Since there are basically no existing WebSockets servers, there is no compatibility reason to allow ws:// (as opposed to wss//) WebSockets from an https:// webpage. We would like to deliver wss for HTTPS page