New novnc websockify wrapper

Added novnc proxy supporting new websockify versions

The websockify library starting from this commit:

https://github.com/kanaka/websockify/commit/7b3dd8a6f5ef26dbfd6c34a91600ea1613aefaa2

separates WebSocketProxy from the handler class

The `NovaWebSocketProxy` class defined in console/webvirtmgr-novnc inherit from `WebSocketProxy` and still seems to work but its `new_client` method never gets called.

This commit adds a new script that can be used with the new websockify library.