When `utils/launch.sh` clones websockify, it can be cloned
into the incorrect directory, depending on how `utils/launch.sh`
is run.  This commit ensures that websockify is always cloned into
`utils/websockify`.

Relies on the libraries chai and mocha (available via npm from Node.JS).

Add anything installed via npm to the .gitignore file.

Also, update nova-novncproxy to import websockify instead of wsproxy.

No sequence numbering and only support b64encoding at the moment.